cfq-iosched.c

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/*
 *  CFQ, or complete fairness queueing, disk scheduler.
 *
 *  Based on ideas from a previously unfinished io
 *  scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
 *
 *  Copyright (C) 2003 Jens Axboe <[email protected]>
 */
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/jiffies.h>
#include <linux/rbtree.h>
#include <linux/ioprio.h>
#include <linux/blktrace_api.h>
#include "blk.h"
#include "blk-cgroup.h"

/*
 * tunables
 */
/* max queue in one round of service */
static const int cfq_quantum = 8;
static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
/* maximum backwards seek, in KiB */
static const int cfq_back_max = 16 * 1024;
/* penalty of a backwards seek */
static const int cfq_back_penalty = 2;
static const int cfq_slice_sync = HZ / 10;
static int cfq_slice_async = HZ / 25;
static const int cfq_slice_async_rq = 2;
static int cfq_slice_idle = HZ / 125;
static int cfq_group_idle = HZ / 125;
static const int cfq_target_latency = HZ * 3/10; /* 300 ms */
static const int cfq_hist_divisor = 4;

/*
 * offset from end of service tree
 */
#define CFQ_IDLE_DELAY      (HZ / 5)

/*
 * below this threshold, we consider thinktime immediate
 */
#define CFQ_MIN_TT      (2)

#define CFQ_SLICE_SCALE     (5)
#define CFQ_HW_QUEUE_MIN    (5)
#define CFQ_SERVICE_SHIFT       12

#define CFQQ_SEEK_THR       (sector_t)(8 * 100)
#define CFQQ_CLOSE_THR      (sector_t)(8 * 1024)
#define CFQQ_SECT_THR_NONROT    (sector_t)(2 * 32)
#define CFQQ_SEEKY(cfqq)    (hweight32(cfqq->seek_history) > 32/8)

#define RQ_CIC(rq)      icq_to_cic((rq)->elv.icq)
#define RQ_CFQQ(rq)     (struct cfq_queue *) ((rq)->elv.priv[0])
#define RQ_CFQG(rq)     (struct cfq_group *) ((rq)->elv.priv[1])

static struct kmem_cache *cfq_pool;

#define CFQ_PRIO_LISTS      IOPRIO_BE_NR
#define cfq_class_idle(cfqq)    ((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
#define cfq_class_rt(cfqq)  ((cfqq)->ioprio_class == IOPRIO_CLASS_RT)

#define sample_valid(samples)   ((samples) > 80)
#define rb_entry_cfqg(node) rb_entry((node), struct cfq_group, rb_node)

struct cfq_ttime {
    unsigned long last_end_request;

    unsigned long ttime_total;
    unsigned long ttime_samples;
    unsigned long ttime_mean;
};

/*
 * Most of our rbtree usage is for sorting with min extraction, so
 * if we cache the leftmost node we don't have to walk down the tree
 * to find it. Idea borrowed from Ingo Molnars CFS scheduler. We should
 * move this into the elevator for the rq sorting as well.
 */
struct cfq_rb_root {
    struct rb_root rb;
    struct rb_node *left;
    unsigned count;
    unsigned total_weight;
    u64 min_vdisktime;
    struct cfq_ttime ttime;
};
#define CFQ_RB_ROOT (struct cfq_rb_root) { .rb = RB_ROOT, \
            .ttime = {.last_end_request = jiffies,},}

/*
 * Per process-grouping structure
 */
struct cfq_queue {
    /* reference count */
    int ref;
    /* various state flags, see below */
    unsigned int flags;
    /* parent cfq_data */
    struct cfq_data *cfqd;
    /* service_tree member */
    struct rb_node rb_node;
    /* service_tree key */
    unsigned long rb_key;
    /* prio tree member */
    struct rb_node p_node;
    /* prio tree root we belong to, if any */
    struct rb_root *p_root;
    /* sorted list of pending requests */
    struct rb_root sort_list;
    /* if fifo isn't expired, next request to serve */
    struct request *next_rq;
    /* requests queued in sort_list */
    int queued[2];
    /* currently allocated requests */
    int allocated[2];
    /* fifo list of requests in sort_list */
    struct list_head fifo;

    /* time when queue got scheduled in to dispatch first request. */
    unsigned long dispatch_start;
    unsigned int allocated_slice;
    unsigned int slice_dispatch;
    /* time when first request from queue completed and slice started. */
    unsigned long slice_start;
    unsigned long slice_end;
    long slice_resid;

    /* pending priority requests */
    int prio_pending;
    /* number of requests that are on the dispatch list or inside driver */
    int dispatched;

    /* io prio of this group */
    unsigned short ioprio, org_ioprio;
    unsigned short ioprio_class;

    pid_t pid;

    u32 seek_history;
    sector_t last_request_pos;

    struct cfq_rb_root *service_tree;
    struct cfq_queue *new_cfqq;
    struct cfq_group *cfqg;
    /* Number of sectors dispatched from queue in single dispatch round */
    unsigned long nr_sectors;
};

/*
 * First index in the service_trees.
 * IDLE is handled separately, so it has negative index
 */
enum wl_prio_t {
    BE_WORKLOAD = 0,
    RT_WORKLOAD = 1,
    IDLE_WORKLOAD = 2,
    CFQ_PRIO_NR,
};

/*
 * Second index in the service_trees.
 */
enum wl_type_t {
    ASYNC_WORKLOAD = 0,
    SYNC_NOIDLE_WORKLOAD = 1,
    SYNC_WORKLOAD = 2
};

struct cfqg_stats {
#ifdef CONFIG_CFQ_GROUP_IOSCHED
    /* total bytes transferred */
    struct blkg_rwstat      service_bytes;
    /* total IOs serviced, post merge */
    struct blkg_rwstat      serviced;
    /* number of ios merged */
    struct blkg_rwstat      merged;
    /* total time spent on device in ns, may not be accurate w/ queueing */
    struct blkg_rwstat      service_time;
    /* total time spent waiting in scheduler queue in ns */
    struct blkg_rwstat      wait_time;
    /* number of IOs queued up */
    struct blkg_rwstat      queued;
    /* total sectors transferred */
    struct blkg_stat        sectors;
    /* total disk time and nr sectors dispatched by this group */
    struct blkg_stat        time;
#ifdef CONFIG_DEBUG_BLK_CGROUP
    /* time not charged to this cgroup */
    struct blkg_stat        unaccounted_time;
    /* sum of number of ios queued across all samples */
    struct blkg_stat        avg_queue_size_sum;
    /* count of samples taken for average */
    struct blkg_stat        avg_queue_size_samples;
    /* how many times this group has been removed from service tree */
    struct blkg_stat        dequeue;
    /* total time spent waiting for it to be assigned a timeslice. */
    struct blkg_stat        group_wait_time;
    /* time spent idling for this blkcg_gq */
    struct blkg_stat        idle_time;
    /* total time with empty current active q with other requests queued */
    struct blkg_stat        empty_time;
    /* fields after this shouldn't be cleared on stat reset */
    uint64_t            start_group_wait_time;
    uint64_t            start_idle_time;
    uint64_t            start_empty_time;
    uint16_t            flags;
#endif  /* CONFIG_DEBUG_BLK_CGROUP */
#endif  /* CONFIG_CFQ_GROUP_IOSCHED */
};

/* This is per cgroup per device grouping structure */
struct cfq_group {
    /* must be the first member */
    struct blkg_policy_data pd;

    /* group service_tree member */
    struct rb_node rb_node;

    /* group service_tree key */
    u64 vdisktime;
    unsigned int weight;
    unsigned int new_weight;
    unsigned int dev_weight;

    /* number of cfqq currently on this group */
    int nr_cfqq;

    /*
     * Per group busy queues average. Useful for workload slice calc. We
     * create the array for each prio class but at run time it is used
     * only for RT and BE class and slot for IDLE class remains unused.
     * This is primarily done to avoid confusion and a gcc warning.
     */
    unsigned int busy_queues_avg[CFQ_PRIO_NR];
    /*
     * rr lists of queues with requests. We maintain service trees for
     * RT and BE classes. These trees are subdivided in subclasses
     * of SYNC, SYNC_NOIDLE and ASYNC based on workload type. For IDLE
     * class there is no subclassification and all the cfq queues go on
     * a single tree service_tree_idle.
     * Counts are embedded in the cfq_rb_root
     */
    struct cfq_rb_root service_trees[2][3];
    struct cfq_rb_root service_tree_idle;

    unsigned long saved_workload_slice;
    enum wl_type_t saved_workload;
    enum wl_prio_t saved_serving_prio;

    /* number of requests that are on the dispatch list or inside driver */
    int dispatched;
    struct cfq_ttime ttime;
    struct cfqg_stats stats;
};

struct cfq_io_cq {
    struct io_cq        icq;        /* must be the first member */
    struct cfq_queue    *cfqq[2];
    struct cfq_ttime    ttime;
    int         ioprio;     /* the current ioprio */
#ifdef CONFIG_CFQ_GROUP_IOSCHED
    uint64_t        blkcg_id;   /* the current blkcg ID */
#endif
};

/*
 * Per block device queue structure
 */
struct cfq_data {
    struct request_queue *queue;
    /* Root service tree for cfq_groups */
    struct cfq_rb_root grp_service_tree;
    struct cfq_group *root_group;

    /*
     * The priority currently being served
     */
    enum wl_prio_t serving_prio;
    enum wl_type_t serving_type;
    unsigned long workload_expires;
    struct cfq_group *serving_group;

    /*
     * Each priority tree is sorted by next_request position.  These
     * trees are used when determining if two or more queues are
     * interleaving requests (see cfq_close_cooperator).
     */
    struct rb_root prio_trees[CFQ_PRIO_LISTS];

    unsigned int busy_queues;
    unsigned int busy_sync_queues;

    int rq_in_driver;
    int rq_in_flight[2];

    /*
     * queue-depth detection
     */
    int rq_queued;
    int hw_tag;
    /*
     * hw_tag can be
     * -1 => indeterminate, (cfq will behave as if NCQ is present, to allow better detection)
     *  1 => NCQ is present (hw_tag_est_depth is the estimated max depth)
     *  0 => no NCQ
     */
    int hw_tag_est_depth;
    unsigned int hw_tag_samples;

    /*
     * idle window management
     */
    struct timer_list idle_slice_timer;
    struct work_struct unplug_work;

    struct cfq_queue *active_queue;
    struct cfq_io_cq *active_cic;

    /*
     * async queue for each priority case
     */
    struct cfq_queue *async_cfqq[2][IOPRIO_BE_NR];
    struct cfq_queue *async_idle_cfqq;

    sector_t last_position;

    /*
     * tunables, see top of file
     */
    unsigned int cfq_quantum;
    unsigned int cfq_fifo_expire[2];
    unsigned int cfq_back_penalty;
    unsigned int cfq_back_max;
    unsigned int cfq_slice[2];
    unsigned int cfq_slice_async_rq;
    unsigned int cfq_slice_idle;
    unsigned int cfq_group_idle;
    unsigned int cfq_latency;
    unsigned int cfq_target_latency;

    /*
     * Fallback dummy cfqq for extreme OOM conditions
     */
    struct cfq_queue oom_cfqq;

    unsigned long last_delayed_sync;
};

static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd);

static struct cfq_rb_root *service_tree_for(struct cfq_group *cfqg,
                        enum wl_prio_t prio,
                        enum wl_type_t type)
{
    if (!cfqg)
        return NULL;

    if (prio == IDLE_WORKLOAD)
        return &cfqg->service_tree_idle;

    return &cfqg->service_trees[prio][type];
}

enum cfqq_state_flags {
    CFQ_CFQQ_FLAG_on_rr = 0,    /* on round-robin busy list */
    CFQ_CFQQ_FLAG_wait_request, /* waiting for a request */
    CFQ_CFQQ_FLAG_must_dispatch,    /* must be allowed a dispatch */
    CFQ_CFQQ_FLAG_must_alloc_slice, /* per-slice must_alloc flag */
    CFQ_CFQQ_FLAG_fifo_expire,  /* FIFO checked in this slice */
    CFQ_CFQQ_FLAG_idle_window,  /* slice idling enabled */
    CFQ_CFQQ_FLAG_prio_changed, /* task priority has changed */
    CFQ_CFQQ_FLAG_slice_new,    /* no requests dispatched in slice */
    CFQ_CFQQ_FLAG_sync,     /* synchronous queue */
    CFQ_CFQQ_FLAG_coop,     /* cfqq is shared */
    CFQ_CFQQ_FLAG_split_coop,   /* shared cfqq will be splitted */
    CFQ_CFQQ_FLAG_deep,     /* sync cfqq experienced large depth */
    CFQ_CFQQ_FLAG_wait_busy,    /* Waiting for next request */
};

#define CFQ_CFQQ_FNS(name)                      \
static inline void cfq_mark_cfqq_##name(struct cfq_queue *cfqq)     \
{                                   \
    (cfqq)->flags |= (1 << CFQ_CFQQ_FLAG_##name);           \
}                                   \
static inline void cfq_clear_cfqq_##name(struct cfq_queue *cfqq)    \
{                                   \
    (cfqq)->flags &= ~(1 << CFQ_CFQQ_FLAG_##name);          \
}                                   \
static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq)     \
{                                   \
    return ((cfqq)->flags & (1 << CFQ_CFQQ_FLAG_##name)) != 0;  \
}

CFQ_CFQQ_FNS(on_rr);
CFQ_CFQQ_FNS(wait_request);
CFQ_CFQQ_FNS(must_dispatch);
CFQ_CFQQ_FNS(must_alloc_slice);
CFQ_CFQQ_FNS(fifo_expire);
CFQ_CFQQ_FNS(idle_window);
CFQ_CFQQ_FNS(prio_changed);
CFQ_CFQQ_FNS(slice_new);
CFQ_CFQQ_FNS(sync);
CFQ_CFQQ_FNS(coop);
CFQ_CFQQ_FNS(split_coop);
CFQ_CFQQ_FNS(deep);
CFQ_CFQQ_FNS(wait_busy);
#undef CFQ_CFQQ_FNS

static inline struct cfq_group *pd_to_cfqg(struct blkg_policy_data *pd)
{
    return pd ? container_of(pd, struct cfq_group, pd) : NULL;
}

static inline struct blkcg_gq *cfqg_to_blkg(struct cfq_group *cfqg)
{
    return pd_to_blkg(&cfqg->pd);
}

#if defined(CONFIG_CFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)

/* cfqg stats flags */
enum cfqg_stats_flags {
    CFQG_stats_waiting = 0,
    CFQG_stats_idling,
    CFQG_stats_empty,
};

#define CFQG_FLAG_FNS(name)                     \
static inline void cfqg_stats_mark_##name(struct cfqg_stats *stats) \
{                                   \
    stats->flags |= (1 << CFQG_stats_##name);           \
}                                   \
static inline void cfqg_stats_clear_##name(struct cfqg_stats *stats)    \
{                                   \
    stats->flags &= ~(1 << CFQG_stats_##name);          \
}                                   \
static inline int cfqg_stats_##name(struct cfqg_stats *stats)       \
{                                   \
    return (stats->flags & (1 << CFQG_stats_##name)) != 0;      \
}                                   \

CFQG_FLAG_FNS(waiting)
CFQG_FLAG_FNS(idling)
CFQG_FLAG_FNS(empty)
#undef CFQG_FLAG_FNS

/* This should be called with the queue_lock held. */
static void cfqg_stats_update_group_wait_time(struct cfqg_stats *stats)
{
    unsigned long long now;

    if (!cfqg_stats_waiting(stats))
        return;

    now = sched_clock();
    if (time_after64(now, stats->start_group_wait_time))
        blkg_stat_add(&stats->group_wait_time,
                  now - stats->start_group_wait_time);
    cfqg_stats_clear_waiting(stats);
}

/* This should be called with the queue_lock held. */
static void cfqg_stats_set_start_group_wait_time(struct cfq_group *cfqg,
                         struct cfq_group *curr_cfqg)
{
    struct cfqg_stats *stats = &cfqg->stats;

    if (cfqg_stats_waiting(stats))
        return;
    if (cfqg == curr_cfqg)
        return;
    stats->start_group_wait_time = sched_clock();
    cfqg_stats_mark_waiting(stats);
}

/* This should be called with the queue_lock held. */
static void cfqg_stats_end_empty_time(struct cfqg_stats *stats)
{
    unsigned long long now;

    if (!cfqg_stats_empty(stats))
        return;

    now = sched_clock();
    if (time_after64(now, stats->start_empty_time))
        blkg_stat_add(&stats->empty_time,
                  now - stats->start_empty_time);
    cfqg_stats_clear_empty(stats);
}

static void cfqg_stats_update_dequeue(struct cfq_group *cfqg)
{
    blkg_stat_add(&cfqg->stats.dequeue, 1);
}

static void cfqg_stats_set_start_empty_time(struct cfq_group *cfqg)
{
    struct cfqg_stats *stats = &cfqg->stats;

    if (blkg_rwstat_sum(&stats->queued))
        return;

    /*
     * group is already marked empty. This can happen if cfqq got new
     * request in parent group and moved to this group while being added
     * to service tree. Just ignore the event and move on.
     */
    if (cfqg_stats_empty(stats))
        return;

    stats->start_empty_time = sched_clock();
    cfqg_stats_mark_empty(stats);
}

static void cfqg_stats_update_idle_time(struct cfq_group *cfqg)
{
    struct cfqg_stats *stats = &cfqg->stats;

    if (cfqg_stats_idling(stats)) {
        unsigned long long now = sched_clock();

        if (time_after64(now, stats->start_idle_time))
            blkg_stat_add(&stats->idle_time,
                      now - stats->start_idle_time);
        cfqg_stats_clear_idling(stats);
    }
}

static void cfqg_stats_set_start_idle_time(struct cfq_group *cfqg)
{
    struct cfqg_stats *stats = &cfqg->stats;

    BUG_ON(cfqg_stats_idling(stats));

    stats->start_idle_time = sched_clock();
    cfqg_stats_mark_idling(stats);
}

static void cfqg_stats_update_avg_queue_size(struct cfq_group *cfqg)
{
    struct cfqg_stats *stats = &cfqg->stats;

    blkg_stat_add(&stats->avg_queue_size_sum,
              blkg_rwstat_sum(&stats->queued));
    blkg_stat_add(&stats->avg_queue_size_samples, 1);
    cfqg_stats_update_group_wait_time(stats);
}

#else   /* CONFIG_CFQ_GROUP_IOSCHED && CONFIG_DEBUG_BLK_CGROUP */

static inline void cfqg_stats_set_start_group_wait_time(struct cfq_group *cfqg, struct cfq_group *curr_cfqg) { }
static inline void cfqg_stats_end_empty_time(struct cfqg_stats *stats) { }
static inline void cfqg_stats_update_dequeue(struct cfq_group *cfqg) { }
static inline void cfqg_stats_set_start_empty_time(struct cfq_group *cfqg) { }
static inline void cfqg_stats_update_idle_time(struct cfq_group *cfqg) { }
static inline void cfqg_stats_set_start_idle_time(struct cfq_group *cfqg) { }
static inline void cfqg_stats_update_avg_queue_size(struct cfq_group *cfqg) { }

#endif  /* CONFIG_CFQ_GROUP_IOSCHED && CONFIG_DEBUG_BLK_CGROUP */

#ifdef CONFIG_CFQ_GROUP_IOSCHED

static struct blkcg_policy blkcg_policy_cfq;

static inline struct cfq_group *blkg_to_cfqg(struct blkcg_gq *blkg)
{
    return pd_to_cfqg(blkg_to_pd(blkg, &blkcg_policy_cfq));
}

static inline void cfqg_get(struct cfq_group *cfqg)
{
    return blkg_get(cfqg_to_blkg(cfqg));
}

static inline void cfqg_put(struct cfq_group *cfqg)
{
    return blkg_put(cfqg_to_blkg(cfqg));
}

#define cfq_log_cfqq(cfqd, cfqq, fmt, args...)  do {            \
    char __pbuf[128];                       \
                                    \
    blkg_path(cfqg_to_blkg((cfqq)->cfqg), __pbuf, sizeof(__pbuf));  \
    blk_add_trace_msg((cfqd)->queue, "cfq%d%c %s " fmt, (cfqq)->pid, \
              cfq_cfqq_sync((cfqq)) ? 'S' : 'A',        \
              __pbuf, ##args);              \
} while (0)

#define cfq_log_cfqg(cfqd, cfqg, fmt, args...)  do {            \
    char __pbuf[128];                       \
                                    \
    blkg_path(cfqg_to_blkg(cfqg), __pbuf, sizeof(__pbuf));      \
    blk_add_trace_msg((cfqd)->queue, "%s " fmt, __pbuf, ##args);    \
} while (0)

static inline void cfqg_stats_update_io_add(struct cfq_group *cfqg,
                        struct cfq_group *curr_cfqg, int rw)
{
    blkg_rwstat_add(&cfqg->stats.queued, rw, 1);
    cfqg_stats_end_empty_time(&cfqg->stats);
    cfqg_stats_set_start_group_wait_time(cfqg, curr_cfqg);
}

static inline void cfqg_stats_update_timeslice_used(struct cfq_group *cfqg,
            unsigned long time, unsigned long unaccounted_time)
{
    blkg_stat_add(&cfqg->stats.time, time);
#ifdef CONFIG_DEBUG_BLK_CGROUP
    blkg_stat_add(&cfqg->stats.unaccounted_time, unaccounted_time);
#endif
}

static inline void cfqg_stats_update_io_remove(struct cfq_group *cfqg, int rw)
{
    blkg_rwstat_add(&cfqg->stats.queued, rw, -1);
}

static inline void cfqg_stats_update_io_merged(struct cfq_group *cfqg, int rw)
{
    blkg_rwstat_add(&cfqg->stats.merged, rw, 1);
}

static inline void cfqg_stats_update_dispatch(struct cfq_group *cfqg,
                          uint64_t bytes, int rw)
{
    blkg_stat_add(&cfqg->stats.sectors, bytes >> 9);
    blkg_rwstat_add(&cfqg->stats.serviced, rw, 1);
    blkg_rwstat_add(&cfqg->stats.service_bytes, rw, bytes);
}

static inline void cfqg_stats_update_completion(struct cfq_group *cfqg,
            uint64_t start_time, uint64_t io_start_time, int rw)
{
    struct cfqg_stats *stats = &cfqg->stats;
    unsigned long long now = sched_clock();

    if (time_after64(now, io_start_time))
        blkg_rwstat_add(&stats->service_time, rw, now - io_start_time);
    if (time_after64(io_start_time, start_time))
        blkg_rwstat_add(&stats->wait_time, rw,
                io_start_time - start_time);
}

static void cfq_pd_reset_stats(struct blkcg_gq *blkg)
{
    struct cfq_group *cfqg = blkg_to_cfqg(blkg);
    struct cfqg_stats *stats = &cfqg->stats;

    /* queued stats shouldn't be cleared */
    blkg_rwstat_reset(&stats->service_bytes);
    blkg_rwstat_reset(&stats->serviced);
    blkg_rwstat_reset(&stats->merged);
    blkg_rwstat_reset(&stats->service_time);
    blkg_rwstat_reset(&stats->wait_time);
    blkg_stat_reset(&stats->time);
#ifdef CONFIG_DEBUG_BLK_CGROUP
    blkg_stat_reset(&stats->unaccounted_time);
    blkg_stat_reset(&stats->avg_queue_size_sum);
    blkg_stat_reset(&stats->avg_queue_size_samples);
    blkg_stat_reset(&stats->dequeue);
    blkg_stat_reset(&stats->group_wait_time);
    blkg_stat_reset(&stats->idle_time);
    blkg_stat_reset(&stats->empty_time);
#endif
}

#else   /* CONFIG_CFQ_GROUP_IOSCHED */

static inline void cfqg_get(struct cfq_group *cfqg) { }
static inline void cfqg_put(struct cfq_group *cfqg) { }

#define cfq_log_cfqq(cfqd, cfqq, fmt, args...)  \
    blk_add_trace_msg((cfqd)->queue, "cfq%d " fmt, (cfqq)->pid, ##args)
#define cfq_log_cfqg(cfqd, cfqg, fmt, args...)      do {} while (0)

static inline void cfqg_stats_update_io_add(struct cfq_group *cfqg,
            struct cfq_group *curr_cfqg, int rw) { }
static inline void cfqg_stats_update_timeslice_used(struct cfq_group *cfqg,
            unsigned long time, unsigned long unaccounted_time) { }
static inline void cfqg_stats_update_io_remove(struct cfq_group *cfqg, int rw) { }
static inline void cfqg_stats_update_io_merged(struct cfq_group *cfqg, int rw) { }
static inline void cfqg_stats_update_dispatch(struct cfq_group *cfqg,
                          uint64_t bytes, int rw) { }
static inline void cfqg_stats_update_completion(struct cfq_group *cfqg,
            uint64_t start_time, uint64_t io_start_time, int rw) { }

#endif  /* CONFIG_CFQ_GROUP_IOSCHED */

#define cfq_log(cfqd, fmt, args...) \
    blk_add_trace_msg((cfqd)->queue, "cfq " fmt, ##args)

/* Traverses through cfq group service trees */
#define for_each_cfqg_st(cfqg, i, j, st) \
    for (i = 0; i <= IDLE_WORKLOAD; i++) \
        for (j = 0, st = i < IDLE_WORKLOAD ? &cfqg->service_trees[i][j]\
            : &cfqg->service_tree_idle; \
            (i < IDLE_WORKLOAD && j <= SYNC_WORKLOAD) || \
            (i == IDLE_WORKLOAD && j == 0); \
            j++, st = i < IDLE_WORKLOAD ? \
            &cfqg->service_trees[i][j]: NULL) \

static inline bool cfq_io_thinktime_big(struct cfq_data *cfqd,
    struct cfq_ttime *ttime, bool group_idle)
{
    unsigned long slice;
    if (!sample_valid(ttime->ttime_samples))
        return false;
    if (group_idle)
        slice = cfqd->cfq_group_idle;
    else
        slice = cfqd->cfq_slice_idle;
    return ttime->ttime_mean > slice;
}

static inline bool iops_mode(struct cfq_data *cfqd)
{
    /*
     * If we are not idling on queues and it is a NCQ drive, parallel
     * execution of requests is on and measuring time is not possible
     * in most of the cases until and unless we drive shallower queue
     * depths and that becomes a performance bottleneck. In such cases
     * switch to start providing fairness in terms of number of IOs.
     */
    if (!cfqd->cfq_slice_idle && cfqd->hw_tag)
        return true;
    else
        return false;
}

static inline enum wl_prio_t cfqq_prio(struct cfq_queue *cfqq)
{
    if (cfq_class_idle(cfqq))
        return IDLE_WORKLOAD;
    if (cfq_class_rt(cfqq))
        return RT_WORKLOAD;
    return BE_WORKLOAD;
}


static enum wl_type_t cfqq_type(struct cfq_queue *cfqq)
{
    if (!cfq_cfqq_sync(cfqq))
        return ASYNC_WORKLOAD;
    if (!cfq_cfqq_idle_window(cfqq))
        return SYNC_NOIDLE_WORKLOAD;
    return SYNC_WORKLOAD;
}

static inline int cfq_group_busy_queues_wl(enum wl_prio_t wl,
                    struct cfq_data *cfqd,
                    struct cfq_group *cfqg)
{
    if (wl == IDLE_WORKLOAD)
        return cfqg->service_tree_idle.count;

    return cfqg->service_trees[wl][ASYNC_WORKLOAD].count
        + cfqg->service_trees[wl][SYNC_NOIDLE_WORKLOAD].count
        + cfqg->service_trees[wl][SYNC_WORKLOAD].count;
}

static inline int cfqg_busy_async_queues(struct cfq_data *cfqd,
                    struct cfq_group *cfqg)
{
    return cfqg->service_trees[RT_WORKLOAD][ASYNC_WORKLOAD].count
        + cfqg->service_trees[BE_WORKLOAD][ASYNC_WORKLOAD].count;
}

static void cfq_dispatch_insert(struct request_queue *, struct request *);
static struct cfq_queue *cfq_get_queue(struct cfq_data *cfqd, bool is_sync,
                       struct cfq_io_cq *cic, struct bio *bio,
                       gfp_t gfp_mask);

static inline struct cfq_io_cq *icq_to_cic(struct io_cq *icq)
{
    /* cic->icq is the first member, %NULL will convert to %NULL */
    return container_of(icq, struct cfq_io_cq, icq);
}

static inline struct cfq_io_cq *cfq_cic_lookup(struct cfq_data *cfqd,
                           struct io_context *ioc)
{
    if (ioc)
        return icq_to_cic(ioc_lookup_icq(ioc, cfqd->queue));
    return NULL;
}

static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_cq *cic, bool is_sync)
{
    return cic->cfqq[is_sync];
}

static inline void cic_set_cfqq(struct cfq_io_cq *cic, struct cfq_queue *cfqq,
                bool is_sync)
{
    cic->cfqq[is_sync] = cfqq;
}

static inline struct cfq_data *cic_to_cfqd(struct cfq_io_cq *cic)
{
    return cic->icq.q->elevator->elevator_data;
}

/*
 * We regard a request as SYNC, if it's either a read or has the SYNC bit
 * set (in which case it could also be direct WRITE).
 */
static inline bool cfq_bio_sync(struct bio *bio)
{
    return bio_data_dir(bio) == READ || (bio->bi_rw & REQ_SYNC);
}

/*
 * scheduler run of queue, if there are requests pending and no one in the
 * driver that will restart queueing
 */
static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
{
    if (cfqd->busy_queues) {
        cfq_log(cfqd, "schedule dispatch");
        kblockd_schedule_work(cfqd->queue, &cfqd->unplug_work);
    }
}

/*
 * Scale schedule slice based on io priority. Use the sync time slice only
 * if a queue is marked sync and has sync io queued. A sync queue with async
 * io only, should not get full sync slice length.
 */
static inline int cfq_prio_slice(struct cfq_data *cfqd, bool sync,
                 unsigned short prio)
{
    const int base_slice = cfqd->cfq_slice[sync];

    WARN_ON(prio >= IOPRIO_BE_NR);

    return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - prio));
}

static inline int
cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);
}

static inline u64 cfq_scale_slice(unsigned long delta, struct cfq_group *cfqg)
{
    u64 d = delta << CFQ_SERVICE_SHIFT;

    d = d * CFQ_WEIGHT_DEFAULT;
    do_div(d, cfqg->weight);
    return d;
}

static inline u64 max_vdisktime(u64 min_vdisktime, u64 vdisktime)
{
    s64 delta = (s64)(vdisktime - min_vdisktime);
    if (delta > 0)
        min_vdisktime = vdisktime;

    return min_vdisktime;
}

static inline u64 min_vdisktime(u64 min_vdisktime, u64 vdisktime)
{
    s64 delta = (s64)(vdisktime - min_vdisktime);
    if (delta < 0)
        min_vdisktime = vdisktime;

    return min_vdisktime;
}

static void update_min_vdisktime(struct cfq_rb_root *st)
{
    struct cfq_group *cfqg;

    if (st->left) {
        cfqg = rb_entry_cfqg(st->left);
        st->min_vdisktime = max_vdisktime(st->min_vdisktime,
                          cfqg->vdisktime);
    }
}

/*
 * get averaged number of queues of RT/BE priority.
 * average is updated, with a formula that gives more weight to higher numbers,
 * to quickly follows sudden increases and decrease slowly
 */

static inline unsigned cfq_group_get_avg_queues(struct cfq_data *cfqd,
                    struct cfq_group *cfqg, bool rt)
{
    unsigned min_q, max_q;
    unsigned mult  = cfq_hist_divisor - 1;
    unsigned round = cfq_hist_divisor / 2;
    unsigned busy = cfq_group_busy_queues_wl(rt, cfqd, cfqg);

    min_q = min(cfqg->busy_queues_avg[rt], busy);
    max_q = max(cfqg->busy_queues_avg[rt], busy);
    cfqg->busy_queues_avg[rt] = (mult * max_q + min_q + round) /
        cfq_hist_divisor;
    return cfqg->busy_queues_avg[rt];
}

static inline unsigned
cfq_group_slice(struct cfq_data *cfqd, struct cfq_group *cfqg)
{
    struct cfq_rb_root *st = &cfqd->grp_service_tree;

    return cfqd->cfq_target_latency * cfqg->weight / st->total_weight;
}

static inline unsigned
cfq_scaled_cfqq_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    unsigned slice = cfq_prio_to_slice(cfqd, cfqq);
    if (cfqd->cfq_latency) {
        /*
         * interested queues (we consider only the ones with the same
         * priority class in the cfq group)
         */
        unsigned iq = cfq_group_get_avg_queues(cfqd, cfqq->cfqg,
                        cfq_class_rt(cfqq));
        unsigned sync_slice = cfqd->cfq_slice[1];
        unsigned expect_latency = sync_slice * iq;
        unsigned group_slice = cfq_group_slice(cfqd, cfqq->cfqg);

        if (expect_latency > group_slice) {
            unsigned base_low_slice = 2 * cfqd->cfq_slice_idle;
            /* scale low_slice according to IO priority
             * and sync vs async */
            unsigned low_slice =
                min(slice, base_low_slice * slice / sync_slice);
            /* the adapted slice value is scaled to fit all iqs
             * into the target latency */
            slice = max(slice * group_slice / expect_latency,
                    low_slice);
        }
    }
    return slice;
}

static inline void
cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    unsigned slice = cfq_scaled_cfqq_slice(cfqd, cfqq);

    cfqq->slice_start = jiffies;
    cfqq->slice_end = jiffies + slice;
    cfqq->allocated_slice = slice;
    cfq_log_cfqq(cfqd, cfqq, "set_slice=%lu", cfqq->slice_end - jiffies);
}

/*
 * We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
 * isn't valid until the first request from the dispatch is activated
 * and the slice time set.
 */
static inline bool cfq_slice_used(struct cfq_queue *cfqq)
{
    if (cfq_cfqq_slice_new(cfqq))
        return false;
    if (time_before(jiffies, cfqq->slice_end))
        return false;

    return true;
}

/*
 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
 * We choose the request that is closest to the head right now. Distance
 * behind the head is penalized and only allowed to a certain extent.
 */
static struct request *
cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2, sector_t last)
{
    sector_t s1, s2, d1 = 0, d2 = 0;
    unsigned long back_max;
#define CFQ_RQ1_WRAP    0x01 /* request 1 wraps */
#define CFQ_RQ2_WRAP    0x02 /* request 2 wraps */
    unsigned wrap = 0; /* bit mask: requests behind the disk head? */

    if (rq1 == NULL || rq1 == rq2)
        return rq2;
    if (rq2 == NULL)
        return rq1;

    if (rq_is_sync(rq1) != rq_is_sync(rq2))
        return rq_is_sync(rq1) ? rq1 : rq2;

    if ((rq1->cmd_flags ^ rq2->cmd_flags) & REQ_PRIO)
        return rq1->cmd_flags & REQ_PRIO ? rq1 : rq2;

    s1 = blk_rq_pos(rq1);
    s2 = blk_rq_pos(rq2);

    /*
     * by definition, 1KiB is 2 sectors
     */
    back_max = cfqd->cfq_back_max * 2;

    /*
     * Strict one way elevator _except_ in the case where we allow
     * short backward seeks which are biased as twice the cost of a
     * similar forward seek.
     */
    if (s1 >= last)
        d1 = s1 - last;
    else if (s1 + back_max >= last)
        d1 = (last - s1) * cfqd->cfq_back_penalty;
    else
        wrap |= CFQ_RQ1_WRAP;

    if (s2 >= last)
        d2 = s2 - last;
    else if (s2 + back_max >= last)
        d2 = (last - s2) * cfqd->cfq_back_penalty;
    else
        wrap |= CFQ_RQ2_WRAP;

    /* Found required data */

    /*
     * By doing switch() on the bit mask "wrap" we avoid having to
     * check two variables for all permutations: --> faster!
     */
    switch (wrap) {
    case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
        if (d1 < d2)
            return rq1;
        else if (d2 < d1)
            return rq2;
        else {
            if (s1 >= s2)
                return rq1;
            else
                return rq2;
        }

    case CFQ_RQ2_WRAP:
        return rq1;
    case CFQ_RQ1_WRAP:
        return rq2;
    case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both rqs wrapped */
    default:
        /*
         * Since both rqs are wrapped,
         * start with the one that's further behind head
         * (--> only *one* back seek required),
         * since back seek takes more time than forward.
         */
        if (s1 <= s2)
            return rq1;
        else
            return rq2;
    }
}

/*
 * The below is leftmost cache rbtree addon
 */
static struct cfq_queue *cfq_rb_first(struct cfq_rb_root *root)
{
    /* Service tree is empty */
    if (!root->count)
        return NULL;

    if (!root->left)
        root->left = rb_first(&root->rb);

    if (root->left)
        return rb_entry(root->left, struct cfq_queue, rb_node);

    return NULL;
}

static struct cfq_group *cfq_rb_first_group(struct cfq_rb_root *root)
{
    if (!root->left)
        root->left = rb_first(&root->rb);

    if (root->left)
        return rb_entry_cfqg(root->left);

    return NULL;
}

static void rb_erase_init(struct rb_node *n, struct rb_root *root)
{
    rb_erase(n, root);
    RB_CLEAR_NODE(n);
}

static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
{
    if (root->left == n)
        root->left = NULL;
    rb_erase_init(n, &root->rb);
    --root->count;
}

/*
 * would be nice to take fifo expire time into account as well
 */
static struct request *
cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
          struct request *last)
{
    struct rb_node *rbnext = rb_next(&last->rb_node);
    struct rb_node *rbprev = rb_prev(&last->rb_node);
    struct request *next = NULL, *prev = NULL;

    BUG_ON(RB_EMPTY_NODE(&last->rb_node));

    if (rbprev)
        prev = rb_entry_rq(rbprev);

    if (rbnext)
        next = rb_entry_rq(rbnext);
    else {
        rbnext = rb_first(&cfqq->sort_list);
        if (rbnext && rbnext != &last->rb_node)
            next = rb_entry_rq(rbnext);
    }

    return cfq_choose_req(cfqd, next, prev, blk_rq_pos(last));
}

static unsigned long cfq_slice_offset(struct cfq_data *cfqd,
                      struct cfq_queue *cfqq)
{
    /*
     * just an approximation, should be ok.
     */
    return (cfqq->cfqg->nr_cfqq - 1) * (cfq_prio_slice(cfqd, 1, 0) -
               cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio));
}

static inline s64
cfqg_key(struct cfq_rb_root *st, struct cfq_group *cfqg)
{
    return cfqg->vdisktime - st->min_vdisktime;
}

static void
__cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
{
    struct rb_node **node = &st->rb.rb_node;
    struct rb_node *parent = NULL;
    struct cfq_group *__cfqg;
    s64 key = cfqg_key(st, cfqg);
    int left = 1;

    while (*node != NULL) {
        parent = *node;
        __cfqg = rb_entry_cfqg(parent);

        if (key < cfqg_key(st, __cfqg))
            node = &parent->rb_left;
        else {
            node = &parent->rb_right;
            left = 0;
        }
    }

    if (left)
        st->left = &cfqg->rb_node;

    rb_link_node(&cfqg->rb_node, parent, node);
    rb_insert_color(&cfqg->rb_node, &st->rb);
}

static void
cfq_update_group_weight(struct cfq_group *cfqg)
{
    BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node));
    if (cfqg->new_weight) {
        cfqg->weight = cfqg->new_weight;
        cfqg->new_weight = 0;
    }
}

static void
cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
{
    BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node));

    cfq_update_group_weight(cfqg);
    __cfq_group_service_tree_add(st, cfqg);
    st->total_weight += cfqg->weight;
}

static void
cfq_group_notify_queue_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
{
    struct cfq_rb_root *st = &cfqd->grp_service_tree;
    struct cfq_group *__cfqg;
    struct rb_node *n;

    cfqg->nr_cfqq++;
    if (!RB_EMPTY_NODE(&cfqg->rb_node))
        return;

    /*
     * Currently put the group at the end. Later implement something
     * so that groups get lesser vtime based on their weights, so that
     * if group does not loose all if it was not continuously backlogged.
     */
    n = rb_last(&st->rb);
    if (n) {
        __cfqg = rb_entry_cfqg(n);
        cfqg->vdisktime = __cfqg->vdisktime + CFQ_IDLE_DELAY;
    } else
        cfqg->vdisktime = st->min_vdisktime;
    cfq_group_service_tree_add(st, cfqg);
}

static void
cfq_group_service_tree_del(struct cfq_rb_root *st, struct cfq_group *cfqg)
{
    st->total_weight -= cfqg->weight;
    if (!RB_EMPTY_NODE(&cfqg->rb_node))
        cfq_rb_erase(&cfqg->rb_node, st);
}

static void
cfq_group_notify_queue_del(struct cfq_data *cfqd, struct cfq_group *cfqg)
{
    struct cfq_rb_root *st = &cfqd->grp_service_tree;

    BUG_ON(cfqg->nr_cfqq < 1);
    cfqg->nr_cfqq--;

    /* If there are other cfq queues under this group, don't delete it */
    if (cfqg->nr_cfqq)
        return;

    cfq_log_cfqg(cfqd, cfqg, "del_from_rr group");
    cfq_group_service_tree_del(st, cfqg);
    cfqg->saved_workload_slice = 0;
    cfqg_stats_update_dequeue(cfqg);
}

static inline unsigned int cfq_cfqq_slice_usage(struct cfq_queue *cfqq,
                        unsigned int *unaccounted_time)
{
    unsigned int slice_used;

    /*
     * Queue got expired before even a single request completed or
     * got expired immediately after first request completion.
     */
    if (!cfqq->slice_start || cfqq->slice_start == jiffies) {
        /*
         * Also charge the seek time incurred to the group, otherwise
         * if there are mutiple queues in the group, each can dispatch
         * a single request on seeky media and cause lots of seek time
         * and group will never know it.
         */
        slice_used = max_t(unsigned, (jiffies - cfqq->dispatch_start),
                    1);
    } else {
        slice_used = jiffies - cfqq->slice_start;
        if (slice_used > cfqq->allocated_slice) {
            *unaccounted_time = slice_used - cfqq->allocated_slice;
            slice_used = cfqq->allocated_slice;
        }
        if (time_after(cfqq->slice_start, cfqq->dispatch_start))
            *unaccounted_time += cfqq->slice_start -
                    cfqq->dispatch_start;
    }

    return slice_used;
}

static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,
                struct cfq_queue *cfqq)
{
    struct cfq_rb_root *st = &cfqd->grp_service_tree;
    unsigned int used_sl, charge, unaccounted_sl = 0;
    int nr_sync = cfqg->nr_cfqq - cfqg_busy_async_queues(cfqd, cfqg)
            - cfqg->service_tree_idle.count;

    BUG_ON(nr_sync < 0);
    used_sl = charge = cfq_cfqq_slice_usage(cfqq, &unaccounted_sl);

    if (iops_mode(cfqd))
        charge = cfqq->slice_dispatch;
    else if (!cfq_cfqq_sync(cfqq) && !nr_sync)
        charge = cfqq->allocated_slice;

    /* Can't update vdisktime while group is on service tree */
    cfq_group_service_tree_del(st, cfqg);
    cfqg->vdisktime += cfq_scale_slice(charge, cfqg);
    /* If a new weight was requested, update now, off tree */
    cfq_group_service_tree_add(st, cfqg);

    /* This group is being expired. Save the context */
    if (time_after(cfqd->workload_expires, jiffies)) {
        cfqg->saved_workload_slice = cfqd->workload_expires
                        - jiffies;
        cfqg->saved_workload = cfqd->serving_type;
        cfqg->saved_serving_prio = cfqd->serving_prio;
    } else
        cfqg->saved_workload_slice = 0;

    cfq_log_cfqg(cfqd, cfqg, "served: vt=%llu min_vt=%llu", cfqg->vdisktime,
                    st->min_vdisktime);
    cfq_log_cfqq(cfqq->cfqd, cfqq,
             "sl_used=%u disp=%u charge=%u iops=%u sect=%lu",
             used_sl, cfqq->slice_dispatch, charge,
             iops_mode(cfqd), cfqq->nr_sectors);
    cfqg_stats_update_timeslice_used(cfqg, used_sl, unaccounted_sl);
    cfqg_stats_set_start_empty_time(cfqg);
}

static void cfq_init_cfqg_base(struct cfq_group *cfqg)
{
    struct cfq_rb_root *st;
    int i, j;

    for_each_cfqg_st(cfqg, i, j, st)
        *st = CFQ_RB_ROOT;
    RB_CLEAR_NODE(&cfqg->rb_node);

    cfqg->ttime.last_end_request = jiffies;
}

#ifdef CONFIG_CFQ_GROUP_IOSCHED
static void cfq_pd_init(struct blkcg_gq *blkg)
{
    struct cfq_group *cfqg = blkg_to_cfqg(blkg);

    cfq_init_cfqg_base(cfqg);
    cfqg->weight = blkg->blkcg->cfq_weight;
}

/*
 * Search for the cfq group current task belongs to. request_queue lock must
 * be held.
 */
static struct cfq_group *cfq_lookup_create_cfqg(struct cfq_data *cfqd,
                        struct blkcg *blkcg)
{
    struct request_queue *q = cfqd->queue;
    struct cfq_group *cfqg = NULL;

    /* avoid lookup for the common case where there's no blkcg */
    if (blkcg == &blkcg_root) {
        cfqg = cfqd->root_group;
    } else {
        struct blkcg_gq *blkg;

        blkg = blkg_lookup_create(blkcg, q);
        if (!IS_ERR(blkg))
            cfqg = blkg_to_cfqg(blkg);
    }

    return cfqg;
}

static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
{
    /* Currently, all async queues are mapped to root group */
    if (!cfq_cfqq_sync(cfqq))
        cfqg = cfqq->cfqd->root_group;

    cfqq->cfqg = cfqg;
    /* cfqq reference on cfqg */
    cfqg_get(cfqg);
}

static u64 cfqg_prfill_weight_device(struct seq_file *sf,
                     struct blkg_policy_data *pd, int off)
{
    struct cfq_group *cfqg = pd_to_cfqg(pd);

    if (!cfqg->dev_weight)
        return 0;
    return __blkg_prfill_u64(sf, pd, cfqg->dev_weight);
}

static int cfqg_print_weight_device(struct cgroup *cgrp, struct cftype *cft,
                    struct seq_file *sf)
{
    blkcg_print_blkgs(sf, cgroup_to_blkcg(cgrp),
              cfqg_prfill_weight_device, &blkcg_policy_cfq, 0,
              false);
    return 0;
}

static int cfq_print_weight(struct cgroup *cgrp, struct cftype *cft,
                struct seq_file *sf)
{
    seq_printf(sf, "%u\n", cgroup_to_blkcg(cgrp)->cfq_weight);
    return 0;
}

static int cfqg_set_weight_device(struct cgroup *cgrp, struct cftype *cft,
                  const char *buf)
{
    struct blkcg *blkcg = cgroup_to_blkcg(cgrp);
    struct blkg_conf_ctx ctx;
    struct cfq_group *cfqg;
    int ret;

    ret = blkg_conf_prep(blkcg, &blkcg_policy_cfq, buf, &ctx);
    if (ret)
        return ret;

    ret = -EINVAL;
    cfqg = blkg_to_cfqg(ctx.blkg);
    if (!ctx.v || (ctx.v >= CFQ_WEIGHT_MIN && ctx.v <= CFQ_WEIGHT_MAX)) {
        cfqg->dev_weight = ctx.v;
        cfqg->new_weight = cfqg->dev_weight ?: blkcg->cfq_weight;
        ret = 0;
    }

    blkg_conf_finish(&ctx);
    return ret;
}

static int cfq_set_weight(struct cgroup *cgrp, struct cftype *cft, u64 val)
{
    struct blkcg *blkcg = cgroup_to_blkcg(cgrp);
    struct blkcg_gq *blkg;
    struct hlist_node *n;

    if (val < CFQ_WEIGHT_MIN || val > CFQ_WEIGHT_MAX)
        return -EINVAL;

    spin_lock_irq(&blkcg->lock);
    blkcg->cfq_weight = (unsigned int)val;

    hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
        struct cfq_group *cfqg = blkg_to_cfqg(blkg);

        if (cfqg && !cfqg->dev_weight)
            cfqg->new_weight = blkcg->cfq_weight;
    }

    spin_unlock_irq(&blkcg->lock);
    return 0;
}

static int cfqg_print_stat(struct cgroup *cgrp, struct cftype *cft,
               struct seq_file *sf)
{
    struct blkcg *blkcg = cgroup_to_blkcg(cgrp);

    blkcg_print_blkgs(sf, blkcg, blkg_prfill_stat, &blkcg_policy_cfq,
              cft->private, false);
    return 0;
}

static int cfqg_print_rwstat(struct cgroup *cgrp, struct cftype *cft,
                 struct seq_file *sf)
{
    struct blkcg *blkcg = cgroup_to_blkcg(cgrp);

    blkcg_print_blkgs(sf, blkcg, blkg_prfill_rwstat, &blkcg_policy_cfq,
              cft->private, true);
    return 0;
}

#ifdef CONFIG_DEBUG_BLK_CGROUP
static u64 cfqg_prfill_avg_queue_size(struct seq_file *sf,
                      struct blkg_policy_data *pd, int off)
{
    struct cfq_group *cfqg = pd_to_cfqg(pd);
    u64 samples = blkg_stat_read(&cfqg->stats.avg_queue_size_samples);
    u64 v = 0;

    if (samples) {
        v = blkg_stat_read(&cfqg->stats.avg_queue_size_sum);
        do_div(v, samples);
    }
    __blkg_prfill_u64(sf, pd, v);
    return 0;
}

/* print avg_queue_size */
static int cfqg_print_avg_queue_size(struct cgroup *cgrp, struct cftype *cft,
                     struct seq_file *sf)
{
    struct blkcg *blkcg = cgroup_to_blkcg(cgrp);

    blkcg_print_blkgs(sf, blkcg, cfqg_prfill_avg_queue_size,
              &blkcg_policy_cfq, 0, false);
    return 0;
}
#endif  /* CONFIG_DEBUG_BLK_CGROUP */

static struct cftype cfq_blkcg_files[] = {
    {
        .name = "weight_device",
        .read_seq_string = cfqg_print_weight_device,
        .write_string = cfqg_set_weight_device,
        .max_write_len = 256,
    },
    {
        .name = "weight",
        .read_seq_string = cfq_print_weight,
        .write_u64 = cfq_set_weight,
    },
    {
        .name = "time",
        .private = offsetof(struct cfq_group, stats.time),
        .read_seq_string = cfqg_print_stat,
    },
    {
        .name = "sectors",
        .private = offsetof(struct cfq_group, stats.sectors),
        .read_seq_string = cfqg_print_stat,
    },
    {
        .name = "io_service_bytes",
        .private = offsetof(struct cfq_group, stats.service_bytes),
        .read_seq_string = cfqg_print_rwstat,
    },
    {
        .name = "io_serviced",
        .private = offsetof(struct cfq_group, stats.serviced),
        .read_seq_string = cfqg_print_rwstat,
    },
    {
        .name = "io_service_time",
        .private = offsetof(struct cfq_group, stats.service_time),
        .read_seq_string = cfqg_print_rwstat,
    },
    {
        .name = "io_wait_time",
        .private = offsetof(struct cfq_group, stats.wait_time),
        .read_seq_string = cfqg_print_rwstat,
    },
    {
        .name = "io_merged",
        .private = offsetof(struct cfq_group, stats.merged),
        .read_seq_string = cfqg_print_rwstat,
    },
    {
        .name = "io_queued",
        .private = offsetof(struct cfq_group, stats.queued),
        .read_seq_string = cfqg_print_rwstat,
    },
#ifdef CONFIG_DEBUG_BLK_CGROUP
    {
        .name = "avg_queue_size",
        .read_seq_string = cfqg_print_avg_queue_size,
    },
    {
        .name = "group_wait_time",
        .private = offsetof(struct cfq_group, stats.group_wait_time),
        .read_seq_string = cfqg_print_stat,
    },
    {
        .name = "idle_time",
        .private = offsetof(struct cfq_group, stats.idle_time),
        .read_seq_string = cfqg_print_stat,
    },
    {
        .name = "empty_time",
        .private = offsetof(struct cfq_group, stats.empty_time),
        .read_seq_string = cfqg_print_stat,
    },
    {
        .name = "dequeue",
        .private = offsetof(struct cfq_group, stats.dequeue),
        .read_seq_string = cfqg_print_stat,
    },
    {
        .name = "unaccounted_time",
        .private = offsetof(struct cfq_group, stats.unaccounted_time),
        .read_seq_string = cfqg_print_stat,
    },
#endif  /* CONFIG_DEBUG_BLK_CGROUP */
    { } /* terminate */
};
#else /* GROUP_IOSCHED */
static struct cfq_group *cfq_lookup_create_cfqg(struct cfq_data *cfqd,
                        struct blkcg *blkcg)
{
    return cfqd->root_group;
}

static inline void
cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) {
    cfqq->cfqg = cfqg;
}

#endif /* GROUP_IOSCHED */

/*
 * The cfqd->service_trees holds all pending cfq_queue's that have
 * requests waiting to be processed. It is sorted in the order that
 * we will service the queues.
 */
static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                 bool add_front)
{
    struct rb_node **p, *parent;
    struct cfq_queue *__cfqq;
    unsigned long rb_key;
    struct cfq_rb_root *service_tree;
    int left;
    int new_cfqq = 1;

    service_tree = service_tree_for(cfqq->cfqg, cfqq_prio(cfqq),
                        cfqq_type(cfqq));
    if (cfq_class_idle(cfqq)) {
        rb_key = CFQ_IDLE_DELAY;
        parent = rb_last(&service_tree->rb);
        if (parent && parent != &cfqq->rb_node) {
            __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
            rb_key += __cfqq->rb_key;
        } else
            rb_key += jiffies;
    } else if (!add_front) {
        /*
         * Get our rb key offset. Subtract any residual slice
         * value carried from last service. A negative resid
         * count indicates slice overrun, and this should position
         * the next service time further away in the tree.
         */
        rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;
        rb_key -= cfqq->slice_resid;
        cfqq->slice_resid = 0;
    } else {
        rb_key = -HZ;
        __cfqq = cfq_rb_first(service_tree);
        rb_key += __cfqq ? __cfqq->rb_key : jiffies;
    }

    if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
        new_cfqq = 0;
        /*
         * same position, nothing more to do
         */
        if (rb_key == cfqq->rb_key &&
            cfqq->service_tree == service_tree)
            return;

        cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
        cfqq->service_tree = NULL;
    }

    left = 1;
    parent = NULL;
    cfqq->service_tree = service_tree;
    p = &service_tree->rb.rb_node;
    while (*p) {
        struct rb_node **n;

        parent = *p;
        __cfqq = rb_entry(parent, struct cfq_queue, rb_node);

        /*
         * sort by key, that represents service time.
         */
        if (time_before(rb_key, __cfqq->rb_key))
            n = &(*p)->rb_left;
        else {
            n = &(*p)->rb_right;
            left = 0;
        }

        p = n;
    }

    if (left)
        service_tree->left = &cfqq->rb_node;

    cfqq->rb_key = rb_key;
    rb_link_node(&cfqq->rb_node, parent, p);
    rb_insert_color(&cfqq->rb_node, &service_tree->rb);
    service_tree->count++;
    if (add_front || !new_cfqq)
        return;
    cfq_group_notify_queue_add(cfqd, cfqq->cfqg);
}

static struct cfq_queue *
cfq_prio_tree_lookup(struct cfq_data *cfqd, struct rb_root *root,
             sector_t sector, struct rb_node **ret_parent,
             struct rb_node ***rb_link)
{
    struct rb_node **p, *parent;
    struct cfq_queue *cfqq = NULL;

    parent = NULL;
    p = &root->rb_node;
    while (*p) {
        struct rb_node **n;

        parent = *p;
        cfqq = rb_entry(parent, struct cfq_queue, p_node);

        /*
         * Sort strictly based on sector.  Smallest to the left,
         * largest to the right.
         */
        if (sector > blk_rq_pos(cfqq->next_rq))
            n = &(*p)->rb_right;
        else if (sector < blk_rq_pos(cfqq->next_rq))
            n = &(*p)->rb_left;
        else
            break;
        p = n;
        cfqq = NULL;
    }

    *ret_parent = parent;
    if (rb_link)
        *rb_link = p;
    return cfqq;
}

static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    struct rb_node **p, *parent;
    struct cfq_queue *__cfqq;

    if (cfqq->p_root) {
        rb_erase(&cfqq->p_node, cfqq->p_root);
        cfqq->p_root = NULL;
    }

    if (cfq_class_idle(cfqq))
        return;
    if (!cfqq->next_rq)
        return;

    cfqq->p_root = &cfqd->prio_trees[cfqq->org_ioprio];
    __cfqq = cfq_prio_tree_lookup(cfqd, cfqq->p_root,
                      blk_rq_pos(cfqq->next_rq), &parent, &p);
    if (!__cfqq) {
        rb_link_node(&cfqq->p_node, parent, p);
        rb_insert_color(&cfqq->p_node, cfqq->p_root);
    } else
        cfqq->p_root = NULL;
}

/*
 * Update cfqq's position in the service tree.
 */
static void cfq_resort_rr_list(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    /*
     * Resorting requires the cfqq to be on the RR list already.
     */
    if (cfq_cfqq_on_rr(cfqq)) {
        cfq_service_tree_add(cfqd, cfqq, 0);
        cfq_prio_tree_add(cfqd, cfqq);
    }
}

/*
 * add to busy list of queues for service, trying to be fair in ordering
 * the pending list according to last request service
 */
static void cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    cfq_log_cfqq(cfqd, cfqq, "add_to_rr");
    BUG_ON(cfq_cfqq_on_rr(cfqq));
    cfq_mark_cfqq_on_rr(cfqq);
    cfqd->busy_queues++;
    if (cfq_cfqq_sync(cfqq))
        cfqd->busy_sync_queues++;

    cfq_resort_rr_list(cfqd, cfqq);
}

/*
 * Called when the cfqq no longer has requests pending, remove it from
 * the service tree.
 */
static void cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    cfq_log_cfqq(cfqd, cfqq, "del_from_rr");
    BUG_ON(!cfq_cfqq_on_rr(cfqq));
    cfq_clear_cfqq_on_rr(cfqq);

    if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
        cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
        cfqq->service_tree = NULL;
    }
    if (cfqq->p_root) {
        rb_erase(&cfqq->p_node, cfqq->p_root);
        cfqq->p_root = NULL;
    }

    cfq_group_notify_queue_del(cfqd, cfqq->cfqg);
    BUG_ON(!cfqd->busy_queues);
    cfqd->busy_queues--;
    if (cfq_cfqq_sync(cfqq))
        cfqd->busy_sync_queues--;
}

/*
 * rb tree support functions
 */
static void cfq_del_rq_rb(struct request *rq)
{
    struct cfq_queue *cfqq = RQ_CFQQ(rq);
    const int sync = rq_is_sync(rq);

    BUG_ON(!cfqq->queued[sync]);
    cfqq->queued[sync]--;

    elv_rb_del(&cfqq->sort_list, rq);

    if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list)) {
        /*
         * Queue will be deleted from service tree when we actually
         * expire it later. Right now just remove it from prio tree
         * as it is empty.
         */
        if (cfqq->p_root) {
            rb_erase(&cfqq->p_node, cfqq->p_root);
            cfqq->p_root = NULL;
        }
    }
}

static void cfq_add_rq_rb(struct request *rq)
{
    struct cfq_queue *cfqq = RQ_CFQQ(rq);
    struct cfq_data *cfqd = cfqq->cfqd;
    struct request *prev;

    cfqq->queued[rq_is_sync(rq)]++;

    elv_rb_add(&cfqq->sort_list, rq);

    if (!cfq_cfqq_on_rr(cfqq))
        cfq_add_cfqq_rr(cfqd, cfqq);

    /*
     * check if this request is a better next-serve candidate
     */
    prev = cfqq->next_rq;
    cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq, cfqd->last_position);

    /*
     * adjust priority tree position, if ->next_rq changes
     */
    if (prev != cfqq->next_rq)
        cfq_prio_tree_add(cfqd, cfqq);

    BUG_ON(!cfqq->next_rq);
}

static void cfq_reposition_rq_rb(struct cfq_queue *cfqq, struct request *rq)
{
    elv_rb_del(&cfqq->sort_list, rq);
    cfqq->queued[rq_is_sync(rq)]--;
    cfqg_stats_update_io_remove(RQ_CFQG(rq), rq->cmd_flags);
    cfq_add_rq_rb(rq);
    cfqg_stats_update_io_add(RQ_CFQG(rq), cfqq->cfqd->serving_group,
                 rq->cmd_flags);
}

static struct request *
cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)
{
    struct task_struct *tsk = current;
    struct cfq_io_cq *cic;
    struct cfq_queue *cfqq;

    cic = cfq_cic_lookup(cfqd, tsk->io_context);
    if (!cic)
        return NULL;

    cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
    if (cfqq) {
        sector_t sector = bio->bi_sector + bio_sectors(bio);

        return elv_rb_find(&cfqq->sort_list, sector);
    }

    return NULL;
}

static void cfq_activate_request(struct request_queue *q, struct request *rq)
{
    struct cfq_data *cfqd = q->elevator->elevator_data;

    cfqd->rq_in_driver++;
    cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",
                        cfqd->rq_in_driver);

    cfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
}

static void cfq_deactivate_request(struct request_queue *q, struct request *rq)
{
    struct cfq_data *cfqd = q->elevator->elevator_data;

    WARN_ON(!cfqd->rq_in_driver);
    cfqd->rq_in_driver--;
    cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "deactivate rq, drv=%d",
                        cfqd->rq_in_driver);
}

static void cfq_remove_request(struct request *rq)
{
    struct cfq_queue *cfqq = RQ_CFQQ(rq);

    if (cfqq->next_rq == rq)
        cfqq->next_rq = cfq_find_next_rq(cfqq->cfqd, cfqq, rq);

    list_del_init(&rq->queuelist);
    cfq_del_rq_rb(rq);

    cfqq->cfqd->rq_queued--;
    cfqg_stats_update_io_remove(RQ_CFQG(rq), rq->cmd_flags);
    if (rq->cmd_flags & REQ_PRIO) {
        WARN_ON(!cfqq->prio_pending);
        cfqq->prio_pending--;
    }
}

static int cfq_merge(struct request_queue *q, struct request **req,
             struct bio *bio)
{
    struct cfq_data *cfqd = q->elevator->elevator_data;
    struct request *__rq;

    __rq = cfq_find_rq_fmerge(cfqd, bio);
    if (__rq && elv_rq_merge_ok(__rq, bio)) {
        *req = __rq;
        return ELEVATOR_FRONT_MERGE;
    }

    return ELEVATOR_NO_MERGE;
}

static void cfq_merged_request(struct request_queue *q, struct request *req,
                   int type)
{
    if (type == ELEVATOR_FRONT_MERGE) {
        struct cfq_queue *cfqq = RQ_CFQQ(req);

        cfq_reposition_rq_rb(cfqq, req);
    }
}

static void cfq_bio_merged(struct request_queue *q, struct request *req,
                struct bio *bio)
{
    cfqg_stats_update_io_merged(RQ_CFQG(req), bio->bi_rw);
}

static void
cfq_merged_requests(struct request_queue *q, struct request *rq,
            struct request *next)
{
    struct cfq_queue *cfqq = RQ_CFQQ(rq);
    struct cfq_data *cfqd = q->elevator->elevator_data;

    /*
     * reposition in fifo if next is older than rq
     */
    if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
        time_before(rq_fifo_time(next), rq_fifo_time(rq))) {
        list_move(&rq->queuelist, &next->queuelist);
        rq_set_fifo_time(rq, rq_fifo_time(next));
    }

    if (cfqq->next_rq == next)
        cfqq->next_rq = rq;
    cfq_remove_request(next);
    cfqg_stats_update_io_merged(RQ_CFQG(rq), next->cmd_flags);

    cfqq = RQ_CFQQ(next);
    /*
     * all requests of this queue are merged to other queues, delete it
     * from the service tree. If it's the active_queue,
     * cfq_dispatch_requests() will choose to expire it or do idle
     */
    if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list) &&
        cfqq != cfqd->active_queue)
        cfq_del_cfqq_rr(cfqd, cfqq);
}

static int cfq_allow_merge(struct request_queue *q, struct request *rq,
               struct bio *bio)
{
    struct cfq_data *cfqd = q->elevator->elevator_data;
    struct cfq_io_cq *cic;
    struct cfq_queue *cfqq;

    /*
     * Disallow merge of a sync bio into an async request.
     */
    if (cfq_bio_sync(bio) && !rq_is_sync(rq))
        return false;

    /*
     * Lookup the cfqq that this bio will be queued with and allow
     * merge only if rq is queued there.
     */
    cic = cfq_cic_lookup(cfqd, current->io_context);
    if (!cic)
        return false;

    cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
    return cfqq == RQ_CFQQ(rq);
}

static inline void cfq_del_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    del_timer(&cfqd->idle_slice_timer);
    cfqg_stats_update_idle_time(cfqq->cfqg);
}

static void __cfq_set_active_queue(struct cfq_data *cfqd,
                   struct cfq_queue *cfqq)
{
    if (cfqq) {
        cfq_log_cfqq(cfqd, cfqq, "set_active wl_prio:%d wl_type:%d",
                cfqd->serving_prio, cfqd->serving_type);
        cfqg_stats_update_avg_queue_size(cfqq->cfqg);
        cfqq->slice_start = 0;
        cfqq->dispatch_start = jiffies;
        cfqq->allocated_slice = 0;
        cfqq->slice_end = 0;
        cfqq->slice_dispatch = 0;
        cfqq->nr_sectors = 0;

        cfq_clear_cfqq_wait_request(cfqq);
        cfq_clear_cfqq_must_dispatch(cfqq);
        cfq_clear_cfqq_must_alloc_slice(cfqq);
        cfq_clear_cfqq_fifo_expire(cfqq);
        cfq_mark_cfqq_slice_new(cfqq);

        cfq_del_timer(cfqd, cfqq);
    }

    cfqd->active_queue = cfqq;
}

/*
 * current cfqq expired its slice (or was too idle), select new one
 */
static void
__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
            bool timed_out)
{
    cfq_log_cfqq(cfqd, cfqq, "slice expired t=%d", timed_out);

    if (cfq_cfqq_wait_request(cfqq))
        cfq_del_timer(cfqd, cfqq);

    cfq_clear_cfqq_wait_request(cfqq);
    cfq_clear_cfqq_wait_busy(cfqq);

    /*
     * If this cfqq is shared between multiple processes, check to
     * make sure that those processes are still issuing I/Os within
     * the mean seek distance.  If not, it may be time to break the
     * queues apart again.
     */
    if (cfq_cfqq_coop(cfqq) && CFQQ_SEEKY(cfqq))
        cfq_mark_cfqq_split_coop(cfqq);

    /*
     * store what was left of this slice, if the queue idled/timed out
     */
    if (timed_out) {
        if (cfq_cfqq_slice_new(cfqq))
            cfqq->slice_resid = cfq_scaled_cfqq_slice(cfqd, cfqq);
        else
            cfqq->slice_resid = cfqq->slice_end - jiffies;
        cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid);
    }

    cfq_group_served(cfqd, cfqq->cfqg, cfqq);

    if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
        cfq_del_cfqq_rr(cfqd, cfqq);

    cfq_resort_rr_list(cfqd, cfqq);

    if (cfqq == cfqd->active_queue)
        cfqd->active_queue = NULL;

    if (cfqd->active_cic) {
        put_io_context(cfqd->active_cic->icq.ioc);
        cfqd->active_cic = NULL;
    }
}

static inline void cfq_slice_expired(struct cfq_data *cfqd, bool timed_out)
{
    struct cfq_queue *cfqq = cfqd->active_queue;

    if (cfqq)
        __cfq_slice_expired(cfqd, cfqq, timed_out);
}

/*
 * Get next queue for service. Unless we have a queue preemption,
 * we'll simply select the first cfqq in the service tree.
 */
static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
{
    struct cfq_rb_root *service_tree =
        service_tree_for(cfqd->serving_group, cfqd->serving_prio,
                    cfqd->serving_type);

    if (!cfqd->rq_queued)
        return NULL;

    /* There is nothing to dispatch */
    if (!service_tree)
        return NULL;
    if (RB_EMPTY_ROOT(&service_tree->rb))
        return NULL;
    return cfq_rb_first(service_tree);
}

static struct cfq_queue *cfq_get_next_queue_forced(struct cfq_data *cfqd)
{
    struct cfq_group *cfqg;
    struct cfq_queue *cfqq;
    int i, j;
    struct cfq_rb_root *st;

    if (!cfqd->rq_queued)
        return NULL;

    cfqg = cfq_get_next_cfqg(cfqd);
    if (!cfqg)
        return NULL;

    for_each_cfqg_st(cfqg, i, j, st)
        if ((cfqq = cfq_rb_first(st)) != NULL)
            return cfqq;
    return NULL;
}

/*
 * Get and set a new active queue for service.
 */
static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd,
                          struct cfq_queue *cfqq)
{
    if (!cfqq)
        cfqq = cfq_get_next_queue(cfqd);

    __cfq_set_active_queue(cfqd, cfqq);
    return cfqq;
}

static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
                      struct request *rq)
{
    if (blk_rq_pos(rq) >= cfqd->last_position)
        return blk_rq_pos(rq) - cfqd->last_position;
    else
        return cfqd->last_position - blk_rq_pos(rq);
}

static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                   struct request *rq)
{
    return cfq_dist_from_last(cfqd, rq) <= CFQQ_CLOSE_THR;
}

static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
                    struct cfq_queue *cur_cfqq)
{
    struct rb_root *root = &cfqd->prio_trees[cur_cfqq->org_ioprio];
    struct rb_node *parent, *node;
    struct cfq_queue *__cfqq;
    sector_t sector = cfqd->last_position;

    if (RB_EMPTY_ROOT(root))
        return NULL;

    /*
     * First, if we find a request starting at the end of the last
     * request, choose it.
     */
    __cfqq = cfq_prio_tree_lookup(cfqd, root, sector, &parent, NULL);
    if (__cfqq)
        return __cfqq;

    /*
     * If the exact sector wasn't found, the parent of the NULL leaf
     * will contain the closest sector.
     */
    __cfqq = rb_entry(parent, struct cfq_queue, p_node);
    if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
        return __cfqq;

    if (blk_rq_pos(__cfqq->next_rq) < sector)
        node = rb_next(&__cfqq->p_node);
    else
        node = rb_prev(&__cfqq->p_node);
    if (!node)
        return NULL;

    __cfqq = rb_entry(node, struct cfq_queue, p_node);
    if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
        return __cfqq;

    return NULL;
}

/*
 * cfqd - obvious
 * cur_cfqq - passed in so that we don't decide that the current queue is
 *        closely cooperating with itself.
 *
 * So, basically we're assuming that that cur_cfqq has dispatched at least
 * one request, and that cfqd->last_position reflects a position on the disk
 * associated with the I/O issued by cur_cfqq.  I'm not sure this is a valid
 * assumption.
 */
static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd,
                          struct cfq_queue *cur_cfqq)
{
    struct cfq_queue *cfqq;

    if (cfq_class_idle(cur_cfqq))
        return NULL;
    if (!cfq_cfqq_sync(cur_cfqq))
        return NULL;
    if (CFQQ_SEEKY(cur_cfqq))
        return NULL;

    /*
     * Don't search priority tree if it's the only queue in the group.
     */
    if (cur_cfqq->cfqg->nr_cfqq == 1)
        return NULL;

    /*
     * We should notice if some of the queues are cooperating, eg
     * working closely on the same area of the disk. In that case,
     * we can group them together and don't waste time idling.
     */
    cfqq = cfqq_close(cfqd, cur_cfqq);
    if (!cfqq)
        return NULL;

    /* If new queue belongs to different cfq_group, don't choose it */
    if (cur_cfqq->cfqg != cfqq->cfqg)
        return NULL;

    /*
     * It only makes sense to merge sync queues.
     */
    if (!cfq_cfqq_sync(cfqq))
        return NULL;
    if (CFQQ_SEEKY(cfqq))
        return NULL;

    /*
     * Do not merge queues of different priority classes
     */
    if (cfq_class_rt(cfqq) != cfq_class_rt(cur_cfqq))
        return NULL;

    return cfqq;
}

/*
 * Determine whether we should enforce idle window for this queue.
 */

static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    enum wl_prio_t prio = cfqq_prio(cfqq);
    struct cfq_rb_root *service_tree = cfqq->service_tree;

    BUG_ON(!service_tree);
    BUG_ON(!service_tree->count);

    if (!cfqd->cfq_slice_idle)
        return false;

    /* We never do for idle class queues. */
    if (prio == IDLE_WORKLOAD)
        return false;

    /* We do for queues that were marked with idle window flag. */
    if (cfq_cfqq_idle_window(cfqq) &&
       !(blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag))
        return true;

    /*
     * Otherwise, we do only if they are the last ones
     * in their service tree.
     */
    if (service_tree->count == 1 && cfq_cfqq_sync(cfqq) &&
       !cfq_io_thinktime_big(cfqd, &service_tree->ttime, false))
        return true;
    cfq_log_cfqq(cfqd, cfqq, "Not idling. st->count:%d",
            service_tree->count);
    return false;
}

static void cfq_arm_slice_timer(struct cfq_data *cfqd)
{
    struct cfq_queue *cfqq = cfqd->active_queue;
    struct cfq_io_cq *cic;
    unsigned long sl, group_idle = 0;

    /*
     * SSD device without seek penalty, disable idling. But only do so
     * for devices that support queuing, otherwise we still have a problem
     * with sync vs async workloads.
     */
    if (blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag)
        return;

    WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));
    WARN_ON(cfq_cfqq_slice_new(cfqq));

    /*
     * idle is disabled, either manually or by past process history
     */
    if (!cfq_should_idle(cfqd, cfqq)) {
        /* no queue idling. Check for group idling */
        if (cfqd->cfq_group_idle)
            group_idle = cfqd->cfq_group_idle;
        else
            return;
    }

    /*
     * still active requests from this queue, don't idle
     */
    if (cfqq->dispatched)
        return;

    /*
     * task has exited, don't wait
     */
    cic = cfqd->active_cic;
    if (!cic || !atomic_read(&cic->icq.ioc->active_ref))
        return;

    /*
     * If our average think time is larger than the remaining time
     * slice, then don't idle. This avoids overrunning the allotted
     * time slice.
     */
    if (sample_valid(cic->ttime.ttime_samples) &&
        (cfqq->slice_end - jiffies < cic->ttime.ttime_mean)) {
        cfq_log_cfqq(cfqd, cfqq, "Not idling. think_time:%lu",
                 cic->ttime.ttime_mean);
        return;
    }

    /* There are other queues in the group, don't do group idle */
    if (group_idle && cfqq->cfqg->nr_cfqq > 1)
        return;

    cfq_mark_cfqq_wait_request(cfqq);

    if (group_idle)
        sl = cfqd->cfq_group_idle;
    else
        sl = cfqd->cfq_slice_idle;

    mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
    cfqg_stats_set_start_idle_time(cfqq->cfqg);
    cfq_log_cfqq(cfqd, cfqq, "arm_idle: %lu group_idle: %d", sl,
            group_idle ? 1 : 0);
}

/*
 * Move request from internal lists to the request queue dispatch list.
 */
static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
{
    struct cfq_data *cfqd = q->elevator->elevator_data;
    struct cfq_queue *cfqq = RQ_CFQQ(rq);

    cfq_log_cfqq(cfqd, cfqq, "dispatch_insert");

    cfqq->next_rq = cfq_find_next_rq(cfqd, cfqq, rq);
    cfq_remove_request(rq);
    cfqq->dispatched++;
    (RQ_CFQG(rq))->dispatched++;
    elv_dispatch_sort(q, rq);

    cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]++;
    cfqq->nr_sectors += blk_rq_sectors(rq);
    cfqg_stats_update_dispatch(cfqq->cfqg, blk_rq_bytes(rq), rq->cmd_flags);
}

/*
 * return expired entry, or NULL to just start from scratch in rbtree
 */
static struct request *cfq_check_fifo(struct cfq_queue *cfqq)
{
    struct request *rq = NULL;

    if (cfq_cfqq_fifo_expire(cfqq))
        return NULL;

    cfq_mark_cfqq_fifo_expire(cfqq);

    if (list_empty(&cfqq->fifo))
        return NULL;

    rq = rq_entry_fifo(cfqq->fifo.next);
    if (time_before(jiffies, rq_fifo_time(rq)))
        rq = NULL;

    cfq_log_cfqq(cfqq->cfqd, cfqq, "fifo=%p", rq);
    return rq;
}

static inline int
cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    const int base_rq = cfqd->cfq_slice_async_rq;

    WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);

    return 2 * base_rq * (IOPRIO_BE_NR - cfqq->ioprio);
}

/*
 * Must be called with the queue_lock held.
 */
static int cfqq_process_refs(struct cfq_queue *cfqq)
{
    int process_refs, io_refs;

    io_refs = cfqq->allocated[READ] + cfqq->allocated[WRITE];
    process_refs = cfqq->ref - io_refs;
    BUG_ON(process_refs < 0);
    return process_refs;
}

static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq)
{
    int process_refs, new_process_refs;
    struct cfq_queue *__cfqq;

    /*
     * If there are no process references on the new_cfqq, then it is
     * unsafe to follow the ->new_cfqq chain as other cfqq's in the
     * chain may have dropped their last reference (not just their
     * last process reference).
     */
    if (!cfqq_process_refs(new_cfqq))
        return;

    /* Avoid a circular list and skip interim queue merges */
    while ((__cfqq = new_cfqq->new_cfqq)) {
        if (__cfqq == cfqq)
            return;
        new_cfqq = __cfqq;
    }

    process_refs = cfqq_process_refs(cfqq);
    new_process_refs = cfqq_process_refs(new_cfqq);
    /*
     * If the process for the cfqq has gone away, there is no
     * sense in merging the queues.
     */
    if (process_refs == 0 || new_process_refs == 0)
        return;

    /*
     * Merge in the direction of the lesser amount of work.
     */
    if (new_process_refs >= process_refs) {
        cfqq->new_cfqq = new_cfqq;
        new_cfqq->ref += process_refs;
    } else {
        new_cfqq->new_cfqq = cfqq;
        cfqq->ref += new_process_refs;
    }
}

static enum wl_type_t cfq_choose_wl(struct cfq_data *cfqd,
                struct cfq_group *cfqg, enum wl_prio_t prio)
{
    struct cfq_queue *queue;
    int i;
    bool key_valid = false;
    unsigned long lowest_key = 0;
    enum wl_type_t cur_best = SYNC_NOIDLE_WORKLOAD;

    for (i = 0; i <= SYNC_WORKLOAD; ++i) {
        /* select the one with lowest rb_key */
        queue = cfq_rb_first(service_tree_for(cfqg, prio, i));
        if (queue &&
            (!key_valid || time_before(queue->rb_key, lowest_key))) {
            lowest_key = queue->rb_key;
            cur_best = i;
            key_valid = true;
        }
    }

    return cur_best;
}

static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
{
    unsigned slice;
    unsigned count;
    struct cfq_rb_root *st;
    unsigned group_slice;
    enum wl_prio_t original_prio = cfqd->serving_prio;

    /* Choose next priority. RT > BE > IDLE */
    if (cfq_group_busy_queues_wl(RT_WORKLOAD, cfqd, cfqg))
        cfqd->serving_prio = RT_WORKLOAD;
    else if (cfq_group_busy_queues_wl(BE_WORKLOAD, cfqd, cfqg))
        cfqd->serving_prio = BE_WORKLOAD;
    else {
        cfqd->serving_prio = IDLE_WORKLOAD;
        cfqd->workload_expires = jiffies + 1;
        return;
    }

    if (original_prio != cfqd->serving_prio)
        goto new_workload;

    /*
     * For RT and BE, we have to choose also the type
     * (SYNC, SYNC_NOIDLE, ASYNC), and to compute a workload
     * expiration time
     */
    st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
    count = st->count;

    /*
     * check workload expiration, and that we still have other queues ready
     */
    if (count && !time_after(jiffies, cfqd->workload_expires))
        return;

new_workload:
    /* otherwise select new workload type */
    cfqd->serving_type =
        cfq_choose_wl(cfqd, cfqg, cfqd->serving_prio);
    st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
    count = st->count;

    /*
     * the workload slice is computed as a fraction of target latency
     * proportional to the number of queues in that workload, over
     * all the queues in the same priority class
     */
    group_slice = cfq_group_slice(cfqd, cfqg);

    slice = group_slice * count /
        max_t(unsigned, cfqg->busy_queues_avg[cfqd->serving_prio],
              cfq_group_busy_queues_wl(cfqd->serving_prio, cfqd, cfqg));

    if (cfqd->serving_type == ASYNC_WORKLOAD) {
        unsigned int tmp;

        /*
         * Async queues are currently system wide. Just taking
         * proportion of queues with-in same group will lead to higher
         * async ratio system wide as generally root group is going
         * to have higher weight. A more accurate thing would be to
         * calculate system wide asnc/sync ratio.
         */
        tmp = cfqd->cfq_target_latency *
            cfqg_busy_async_queues(cfqd, cfqg);
        tmp = tmp/cfqd->busy_queues;
        slice = min_t(unsigned, slice, tmp);

        /* async workload slice is scaled down according to
         * the sync/async slice ratio. */
        slice = slice * cfqd->cfq_slice[0] / cfqd->cfq_slice[1];
    } else
        /* sync workload slice is at least 2 * cfq_slice_idle */
        slice = max(slice, 2 * cfqd->cfq_slice_idle);

    slice = max_t(unsigned, slice, CFQ_MIN_TT);
    cfq_log(cfqd, "workload slice:%d", slice);
    cfqd->workload_expires = jiffies + slice;
}

static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
{
    struct cfq_rb_root *st = &cfqd->grp_service_tree;
    struct cfq_group *cfqg;

    if (RB_EMPTY_ROOT(&st->rb))
        return NULL;
    cfqg = cfq_rb_first_group(st);
    update_min_vdisktime(st);
    return cfqg;
}

static void cfq_choose_cfqg(struct cfq_data *cfqd)
{
    struct cfq_group *cfqg = cfq_get_next_cfqg(cfqd);

    cfqd->serving_group = cfqg;

    /* Restore the workload type data */
    if (cfqg->saved_workload_slice) {
        cfqd->workload_expires = jiffies + cfqg->saved_workload_slice;
        cfqd->serving_type = cfqg->saved_workload;
        cfqd->serving_prio = cfqg->saved_serving_prio;
    } else
        cfqd->workload_expires = jiffies - 1;

    choose_service_tree(cfqd, cfqg);
}

/*
 * Select a queue for service. If we have a current active queue,
 * check whether to continue servicing it, or retrieve and set a new one.
 */
static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
{
    struct cfq_queue *cfqq, *new_cfqq = NULL;

    cfqq = cfqd->active_queue;
    if (!cfqq)
        goto new_queue;

    if (!cfqd->rq_queued)
        return NULL;

    /*
     * We were waiting for group to get backlogged. Expire the queue
     */
    if (cfq_cfqq_wait_busy(cfqq) && !RB_EMPTY_ROOT(&cfqq->sort_list))
        goto expire;

    /*
     * The active queue has run out of time, expire it and select new.
     */
    if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq)) {
        /*
         * If slice had not expired at the completion of last request
         * we might not have turned on wait_busy flag. Don't expire
         * the queue yet. Allow the group to get backlogged.
         *
         * The very fact that we have used the slice, that means we
         * have been idling all along on this queue and it should be
         * ok to wait for this request to complete.
         */
        if (cfqq->cfqg->nr_cfqq == 1 && RB_EMPTY_ROOT(&cfqq->sort_list)
            && cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
            cfqq = NULL;
            goto keep_queue;
        } else
            goto check_group_idle;
    }

    /*
     * The active queue has requests and isn't expired, allow it to
     * dispatch.
     */
    if (!RB_EMPTY_ROOT(&cfqq->sort_list))
        goto keep_queue;

    /*
     * If another queue has a request waiting within our mean seek
     * distance, let it run.  The expire code will check for close
     * cooperators and put the close queue at the front of the service
     * tree.  If possible, merge the expiring queue with the new cfqq.
     */
    new_cfqq = cfq_close_cooperator(cfqd, cfqq);
    if (new_cfqq) {
        if (!cfqq->new_cfqq)
            cfq_setup_merge(cfqq, new_cfqq);
        goto expire;
    }

    /*
     * No requests pending. If the active queue still has requests in
     * flight or is idling for a new request, allow either of these
     * conditions to happen (or time out) before selecting a new queue.
     */
    if (timer_pending(&cfqd->idle_slice_timer)) {
        cfqq = NULL;
        goto keep_queue;
    }

    /*
     * This is a deep seek queue, but the device is much faster than
     * the queue can deliver, don't idle
     **/
    if (CFQQ_SEEKY(cfqq) && cfq_cfqq_idle_window(cfqq) &&
        (cfq_cfqq_slice_new(cfqq) ||
        (cfqq->slice_end - jiffies > jiffies - cfqq->slice_start))) {
        cfq_clear_cfqq_deep(cfqq);
        cfq_clear_cfqq_idle_window(cfqq);
    }

    if (cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
        cfqq = NULL;
        goto keep_queue;
    }

    /*
     * If group idle is enabled and there are requests dispatched from
     * this group, wait for requests to complete.
     */
check_group_idle:
    if (cfqd->cfq_group_idle && cfqq->cfqg->nr_cfqq == 1 &&
        cfqq->cfqg->dispatched &&
        !cfq_io_thinktime_big(cfqd, &cfqq->cfqg->ttime, true)) {
        cfqq = NULL;
        goto keep_queue;
    }

expire:
    cfq_slice_expired(cfqd, 0);
new_queue:
    /*
     * Current queue expired. Check if we have to switch to a new
     * service tree
     */
    if (!new_cfqq)
        cfq_choose_cfqg(cfqd);

    cfqq = cfq_set_active_queue(cfqd, new_cfqq);
keep_queue:
    return cfqq;
}

static int __cfq_forced_dispatch_cfqq(struct cfq_queue *cfqq)
{
    int dispatched = 0;

    while (cfqq->next_rq) {
        cfq_dispatch_insert(cfqq->cfqd->queue, cfqq->next_rq);
        dispatched++;
    }

    BUG_ON(!list_empty(&cfqq->fifo));

    /* By default cfqq is not expired if it is empty. Do it explicitly */
    __cfq_slice_expired(cfqq->cfqd, cfqq, 0);
    return dispatched;
}

/*
 * Drain our current requests. Used for barriers and when switching
 * io schedulers on-the-fly.
 */
static int cfq_forced_dispatch(struct cfq_data *cfqd)
{
    struct cfq_queue *cfqq;
    int dispatched = 0;

    /* Expire the timeslice of the current active queue first */
    cfq_slice_expired(cfqd, 0);
    while ((cfqq = cfq_get_next_queue_forced(cfqd)) != NULL) {
        __cfq_set_active_queue(cfqd, cfqq);
        dispatched += __cfq_forced_dispatch_cfqq(cfqq);
    }

    BUG_ON(cfqd->busy_queues);

    cfq_log(cfqd, "forced_dispatch=%d", dispatched);
    return dispatched;
}

static inline bool cfq_slice_used_soon(struct cfq_data *cfqd,
    struct cfq_queue *cfqq)
{
    /* the queue hasn't finished any request, can't estimate */
    if (cfq_cfqq_slice_new(cfqq))
        return true;
    if (time_after(jiffies + cfqd->cfq_slice_idle * cfqq->dispatched,
        cfqq->slice_end))
        return true;

    return false;
}

static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    unsigned int max_dispatch;

    /*
     * Drain async requests before we start sync IO
     */
    if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_flight[BLK_RW_ASYNC])
        return false;

    /*
     * If this is an async queue and we have sync IO in flight, let it wait
     */
    if (cfqd->rq_in_flight[BLK_RW_SYNC] && !cfq_cfqq_sync(cfqq))
        return false;

    max_dispatch = max_t(unsigned int, cfqd->cfq_quantum / 2, 1);
    if (cfq_class_idle(cfqq))
        max_dispatch = 1;

    /*
     * Does this cfqq already have too much IO in flight?
     */
    if (cfqq->dispatched >= max_dispatch) {
        bool promote_sync = false;
        /*
         * idle queue must always only have a single IO in flight
         */
        if (cfq_class_idle(cfqq))
            return false;

        /*
         * If there is only one sync queue
         * we can ignore async queue here and give the sync
         * queue no dispatch limit. The reason is a sync queue can
         * preempt async queue, limiting the sync queue doesn't make
         * sense. This is useful for aiostress test.
         */
        if (cfq_cfqq_sync(cfqq) && cfqd->busy_sync_queues == 1)
            promote_sync = true;

        /*
         * We have other queues, don't allow more IO from this one
         */
        if (cfqd->busy_queues > 1 && cfq_slice_used_soon(cfqd, cfqq) &&
                !promote_sync)
            return false;

        /*
         * Sole queue user, no limit
         */
        if (cfqd->busy_queues == 1 || promote_sync)
            max_dispatch = -1;
        else
            /*
             * Normally we start throttling cfqq when cfq_quantum/2
             * requests have been dispatched. But we can drive
             * deeper queue depths at the beginning of slice
             * subjected to upper limit of cfq_quantum.
             * */
            max_dispatch = cfqd->cfq_quantum;
    }

    /*
     * Async queues must wait a bit before being allowed dispatch.
     * We also ramp up the dispatch depth gradually for async IO,
     * based on the last sync IO we serviced
     */
    if (!cfq_cfqq_sync(cfqq) && cfqd->cfq_latency) {
        unsigned long last_sync = jiffies - cfqd->last_delayed_sync;
        unsigned int depth;

        depth = last_sync / cfqd->cfq_slice[1];
        if (!depth && !cfqq->dispatched)
            depth = 1;
        if (depth < max_dispatch)
            max_dispatch = depth;
    }

    /*
     * If we're below the current max, allow a dispatch
     */
    return cfqq->dispatched < max_dispatch;
}

/*
 * Dispatch a request from cfqq, moving them to the request queue
 * dispatch list.
 */
static bool cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    struct request *rq;

    BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));

    if (!cfq_may_dispatch(cfqd, cfqq))
        return false;

    /*
     * follow expired path, else get first next available
     */
    rq = cfq_check_fifo(cfqq);
    if (!rq)
        rq = cfqq->next_rq;

    /*
     * insert request into driver dispatch list
     */
    cfq_dispatch_insert(cfqd->queue, rq);

    if (!cfqd->active_cic) {
        struct cfq_io_cq *cic = RQ_CIC(rq);

        atomic_long_inc(&cic->icq.ioc->refcount);
        cfqd->active_cic = cic;
    }

    return true;
}

/*
 * Find the cfqq that we need to service and move a request from that to the
 * dispatch list
 */
static int cfq_dispatch_requests(struct request_queue *q, int force)
{
    struct cfq_data *cfqd = q->elevator->elevator_data;
    struct cfq_queue *cfqq;

    if (!cfqd->busy_queues)
        return 0;

    if (unlikely(force))
        return cfq_forced_dispatch(cfqd);

    cfqq = cfq_select_queue(cfqd);
    if (!cfqq)
        return 0;

    /*
     * Dispatch a request from this cfqq, if it is allowed
     */
    if (!cfq_dispatch_request(cfqd, cfqq))
        return 0;

    cfqq->slice_dispatch++;
    cfq_clear_cfqq_must_dispatch(cfqq);

    /*
     * expire an async queue immediately if it has used up its slice. idle
     * queue always expire after 1 dispatch round.
     */
    if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&
        cfqq->slice_dispatch >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
        cfq_class_idle(cfqq))) {
        cfqq->slice_end = jiffies + 1;
        cfq_slice_expired(cfqd, 0);
    }

    cfq_log_cfqq(cfqd, cfqq, "dispatched a request");
    return 1;
}

/*
 * task holds one reference to the queue, dropped when task exits. each rq
 * in-flight on this queue also holds a reference, dropped when rq is freed.
 *
 * Each cfq queue took a reference on the parent group. Drop it now.
 * queue lock must be held here.
 */
static void cfq_put_queue(struct cfq_queue *cfqq)
{
    struct cfq_data *cfqd = cfqq->cfqd;
    struct cfq_group *cfqg;

    BUG_ON(cfqq->ref <= 0);

    cfqq->ref--;
    if (cfqq->ref)
        return;

    cfq_log_cfqq(cfqd, cfqq, "put_queue");
    BUG_ON(rb_first(&cfqq->sort_list));
    BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
    cfqg = cfqq->cfqg;

    if (unlikely(cfqd->active_queue == cfqq)) {
        __cfq_slice_expired(cfqd, cfqq, 0);
        cfq_schedule_dispatch(cfqd);
    }

    BUG_ON(cfq_cfqq_on_rr(cfqq));
    kmem_cache_free(cfq_pool, cfqq);
    cfqg_put(cfqg);
}

static void cfq_put_cooperator(struct cfq_queue *cfqq)
{
    struct cfq_queue *__cfqq, *next;

    /*
     * If this queue was scheduled to merge with another queue, be
     * sure to drop the reference taken on that queue (and others in
     * the merge chain).  See cfq_setup_merge and cfq_merge_cfqqs.
     */
    __cfqq = cfqq->new_cfqq;
    while (__cfqq) {
        if (__cfqq == cfqq) {
            WARN(1, "cfqq->new_cfqq loop detected\n");
            break;
        }
        next = __cfqq->new_cfqq;
        cfq_put_queue(__cfqq);
        __cfqq = next;
    }
}

static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    if (unlikely(cfqq == cfqd->active_queue)) {
        __cfq_slice_expired(cfqd, cfqq, 0);
        cfq_schedule_dispatch(cfqd);
    }

    cfq_put_cooperator(cfqq);

    cfq_put_queue(cfqq);
}

static void cfq_init_icq(struct io_cq *icq)
{
    struct cfq_io_cq *cic = icq_to_cic(icq);

    cic->ttime.last_end_request = jiffies;
}

static void cfq_exit_icq(struct io_cq *icq)
{
    struct cfq_io_cq *cic = icq_to_cic(icq);
    struct cfq_data *cfqd = cic_to_cfqd(cic);

    if (cic->cfqq[BLK_RW_ASYNC]) {
        cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);
        cic->cfqq[BLK_RW_ASYNC] = NULL;
    }

    if (cic->cfqq[BLK_RW_SYNC]) {
        cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_SYNC]);
        cic->cfqq[BLK_RW_SYNC] = NULL;
    }
}

static void cfq_init_prio_data(struct cfq_queue *cfqq, struct cfq_io_cq *cic)
{
    struct task_struct *tsk = current;
    int ioprio_class;

    if (!cfq_cfqq_prio_changed(cfqq))
        return;

    ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio);
    switch (ioprio_class) {
    default:
        printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class);
    case IOPRIO_CLASS_NONE:
        /*
         * no prio set, inherit CPU scheduling settings
         */
        cfqq->ioprio = task_nice_ioprio(tsk);
        cfqq->ioprio_class = task_nice_ioclass(tsk);
        break;
    case IOPRIO_CLASS_RT:
        cfqq->ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
        cfqq->ioprio_class = IOPRIO_CLASS_RT;
        break;
    case IOPRIO_CLASS_BE:
        cfqq->ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
        cfqq->ioprio_class = IOPRIO_CLASS_BE;
        break;
    case IOPRIO_CLASS_IDLE:
        cfqq->ioprio_class = IOPRIO_CLASS_IDLE;
        cfqq->ioprio = 7;
        cfq_clear_cfqq_idle_window(cfqq);
        break;
    }

    /*
     * keep track of original prio settings in case we have to temporarily
     * elevate the priority of this queue
     */
    cfqq->org_ioprio = cfqq->ioprio;
    cfq_clear_cfqq_prio_changed(cfqq);
}

static void check_ioprio_changed(struct cfq_io_cq *cic, struct bio *bio)
{
    int ioprio = cic->icq.ioc->ioprio;
    struct cfq_data *cfqd = cic_to_cfqd(cic);
    struct cfq_queue *cfqq;

    /*
     * Check whether ioprio has changed.  The condition may trigger
     * spuriously on a newly created cic but there's no harm.
     */
    if (unlikely(!cfqd) || likely(cic->ioprio == ioprio))
        return;

    cfqq = cic->cfqq[BLK_RW_ASYNC];
    if (cfqq) {
        struct cfq_queue *new_cfqq;
        new_cfqq = cfq_get_queue(cfqd, BLK_RW_ASYNC, cic, bio,
                     GFP_ATOMIC);
        if (new_cfqq) {
            cic->cfqq[BLK_RW_ASYNC] = new_cfqq;
            cfq_put_queue(cfqq);
        }
    }

    cfqq = cic->cfqq[BLK_RW_SYNC];
    if (cfqq)
        cfq_mark_cfqq_prio_changed(cfqq);

    cic->ioprio = ioprio;
}

static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
              pid_t pid, bool is_sync)
{
    RB_CLEAR_NODE(&cfqq->rb_node);
    RB_CLEAR_NODE(&cfqq->p_node);
    INIT_LIST_HEAD(&cfqq->fifo);

    cfqq->ref = 0;
    cfqq->cfqd = cfqd;

    cfq_mark_cfqq_prio_changed(cfqq);

    if (is_sync) {
        if (!cfq_class_idle(cfqq))
            cfq_mark_cfqq_idle_window(cfqq);
        cfq_mark_cfqq_sync(cfqq);
    }
    cfqq->pid = pid;
}

#ifdef CONFIG_CFQ_GROUP_IOSCHED
static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
{
    struct cfq_data *cfqd = cic_to_cfqd(cic);
    struct cfq_queue *sync_cfqq;
    uint64_t id;

    rcu_read_lock();
    id = bio_blkcg(bio)->id;
    rcu_read_unlock();

    /*
     * Check whether blkcg has changed.  The condition may trigger
     * spuriously on a newly created cic but there's no harm.
     */
    if (unlikely(!cfqd) || likely(cic->blkcg_id == id))
        return;

    sync_cfqq = cic_to_cfqq(cic, 1);
    if (sync_cfqq) {
        /*
         * Drop reference to sync queue. A new sync queue will be
         * assigned in new group upon arrival of a fresh request.
         */
        cfq_log_cfqq(cfqd, sync_cfqq, "changed cgroup");
        cic_set_cfqq(cic, NULL, 1);
        cfq_put_queue(sync_cfqq);
    }

    cic->blkcg_id = id;
}
#else
static inline void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) { }
#endif  /* CONFIG_CFQ_GROUP_IOSCHED */

static struct cfq_queue *
cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
             struct bio *bio, gfp_t gfp_mask)
{
    struct blkcg *blkcg;
    struct cfq_queue *cfqq, *new_cfqq = NULL;
    struct cfq_group *cfqg;

retry:
    rcu_read_lock();

    blkcg = bio_blkcg(bio);
    cfqg = cfq_lookup_create_cfqg(cfqd, blkcg);
    cfqq = cic_to_cfqq(cic, is_sync);

    /*
     * Always try a new alloc if we fell back to the OOM cfqq
     * originally, since it should just be a temporary situation.
     */
    if (!cfqq || cfqq == &cfqd->oom_cfqq) {
        cfqq = NULL;
        if (new_cfqq) {
            cfqq = new_cfqq;
            new_cfqq = NULL;
        } else if (gfp_mask & __GFP_WAIT) {
            rcu_read_unlock();
            spin_unlock_irq(cfqd->queue->queue_lock);
            new_cfqq = kmem_cache_alloc_node(cfq_pool,
                    gfp_mask | __GFP_ZERO,
                    cfqd->queue->node);
            spin_lock_irq(cfqd->queue->queue_lock);
            if (new_cfqq)
                goto retry;
        } else {
            cfqq = kmem_cache_alloc_node(cfq_pool,
                    gfp_mask | __GFP_ZERO,
                    cfqd->queue->node);
        }

        if (cfqq) {
            cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
            cfq_init_prio_data(cfqq, cic);
            cfq_link_cfqq_cfqg(cfqq, cfqg);
            cfq_log_cfqq(cfqd, cfqq, "alloced");
        } else
            cfqq = &cfqd->oom_cfqq;
    }

    if (new_cfqq)
        kmem_cache_free(cfq_pool, new_cfqq);

    rcu_read_unlock();
    return cfqq;
}

static struct cfq_queue **
cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio)
{
    switch (ioprio_class) {
    case IOPRIO_CLASS_RT:
        return &cfqd->async_cfqq[0][ioprio];
    case IOPRIO_CLASS_NONE:
        ioprio = IOPRIO_NORM;
        /* fall through */
    case IOPRIO_CLASS_BE:
        return &cfqd->async_cfqq[1][ioprio];
    case IOPRIO_CLASS_IDLE:
        return &cfqd->async_idle_cfqq;
    default:
        BUG();
    }
}

static struct cfq_queue *
cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
          struct bio *bio, gfp_t gfp_mask)
{
    const int ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio);
    const int ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
    struct cfq_queue **async_cfqq = NULL;
    struct cfq_queue *cfqq = NULL;

    if (!is_sync) {
        async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio);
        cfqq = *async_cfqq;
    }

    if (!cfqq)
        cfqq = cfq_find_alloc_queue(cfqd, is_sync, cic, bio, gfp_mask);

    /*
     * pin the queue now that it's allocated, scheduler exit will prune it
     */
    if (!is_sync && !(*async_cfqq)) {
        cfqq->ref++;
        *async_cfqq = cfqq;
    }

    cfqq->ref++;
    return cfqq;
}

static void
__cfq_update_io_thinktime(struct cfq_ttime *ttime, unsigned long slice_idle)
{
    unsigned long elapsed = jiffies - ttime->last_end_request;
    elapsed = min(elapsed, 2UL * slice_idle);

    ttime->ttime_samples = (7*ttime->ttime_samples + 256) / 8;
    ttime->ttime_total = (7*ttime->ttime_total + 256*elapsed) / 8;
    ttime->ttime_mean = (ttime->ttime_total + 128) / ttime->ttime_samples;
}

static void
cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
            struct cfq_io_cq *cic)
{
    if (cfq_cfqq_sync(cfqq)) {
        __cfq_update_io_thinktime(&cic->ttime, cfqd->cfq_slice_idle);
        __cfq_update_io_thinktime(&cfqq->service_tree->ttime,
            cfqd->cfq_slice_idle);
    }
#ifdef CONFIG_CFQ_GROUP_IOSCHED
    __cfq_update_io_thinktime(&cfqq->cfqg->ttime, cfqd->cfq_group_idle);
#endif
}

static void
cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
               struct request *rq)
{
    sector_t sdist = 0;
    sector_t n_sec = blk_rq_sectors(rq);
    if (cfqq->last_request_pos) {
        if (cfqq->last_request_pos < blk_rq_pos(rq))
            sdist = blk_rq_pos(rq) - cfqq->last_request_pos;
        else
            sdist = cfqq->last_request_pos - blk_rq_pos(rq);
    }

    cfqq->seek_history <<= 1;
    if (blk_queue_nonrot(cfqd->queue))
        cfqq->seek_history |= (n_sec < CFQQ_SECT_THR_NONROT);
    else
        cfqq->seek_history |= (sdist > CFQQ_SEEK_THR);
}

/*
 * Disable idle window if the process thinks too long or seeks so much that
 * it doesn't matter
 */
static void
cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
               struct cfq_io_cq *cic)
{
    int old_idle, enable_idle;

    /*
     * Don't idle for async or idle io prio class
     */
    if (!cfq_cfqq_sync(cfqq) || cfq_class_idle(cfqq))
        return;

    enable_idle = old_idle = cfq_cfqq_idle_window(cfqq);

    if (cfqq->queued[0] + cfqq->queued[1] >= 4)
        cfq_mark_cfqq_deep(cfqq);

    if (cfqq->next_rq && (cfqq->next_rq->cmd_flags & REQ_NOIDLE))
        enable_idle = 0;
    else if (!atomic_read(&cic->icq.ioc->active_ref) ||
         !cfqd->cfq_slice_idle ||
         (!cfq_cfqq_deep(cfqq) && CFQQ_SEEKY(cfqq)))
        enable_idle = 0;
    else if (sample_valid(cic->ttime.ttime_samples)) {
        if (cic->ttime.ttime_mean > cfqd->cfq_slice_idle)
            enable_idle = 0;
        else
            enable_idle = 1;
    }

    if (old_idle != enable_idle) {
        cfq_log_cfqq(cfqd, cfqq, "idle=%d", enable_idle);
        if (enable_idle)
            cfq_mark_cfqq_idle_window(cfqq);
        else
            cfq_clear_cfqq_idle_window(cfqq);
    }
}

/*
 * Check if new_cfqq should preempt the currently active queue. Return 0 for
 * no or if we aren't sure, a 1 will cause a preempt.
 */
static bool
cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
           struct request *rq)
{
    struct cfq_queue *cfqq;

    cfqq = cfqd->active_queue;
    if (!cfqq)
        return false;

    if (cfq_class_idle(new_cfqq))
        return false;

    if (cfq_class_idle(cfqq))
        return true;

    /*
     * Don't allow a non-RT request to preempt an ongoing RT cfqq timeslice.
     */
    if (cfq_class_rt(cfqq) && !cfq_class_rt(new_cfqq))
        return false;

    /*
     * if the new request is sync, but the currently running queue is
     * not, let the sync request have priority.
     */
    if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
        return true;

    if (new_cfqq->cfqg != cfqq->cfqg)
        return false;

    if (cfq_slice_used(cfqq))
        return true;

    /* Allow preemption only if we are idling on sync-noidle tree */
    if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD &&
        cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD &&
        new_cfqq->service_tree->count == 2 &&
        RB_EMPTY_ROOT(&cfqq->sort_list))
        return true;

    /*
     * So both queues are sync. Let the new request get disk time if
     * it's a metadata request and the current queue is doing regular IO.
     */
    if ((rq->cmd_flags & REQ_PRIO) && !cfqq->prio_pending)
        return true;

    /*
     * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
     */
    if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
        return true;

    /* An idle queue should not be idle now for some reason */
    if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq))
        return true;

    if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))
        return false;

    /*
     * if this request is as-good as one we would expect from the
     * current cfqq, let it preempt
     */
    if (cfq_rq_close(cfqd, cfqq, rq))
        return true;

    return false;
}

/*
 * cfqq preempts the active queue. if we allowed preempt with no slice left,
 * let it have half of its nominal slice.
 */
static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    enum wl_type_t old_type = cfqq_type(cfqd->active_queue);

    cfq_log_cfqq(cfqd, cfqq, "preempt");
    cfq_slice_expired(cfqd, 1);

    /*
     * workload type is changed, don't save slice, otherwise preempt
     * doesn't happen
     */
    if (old_type != cfqq_type(cfqq))
        cfqq->cfqg->saved_workload_slice = 0;

    /*
     * Put the new queue at the front of the of the current list,
     * so we know that it will be selected next.
     */
    BUG_ON(!cfq_cfqq_on_rr(cfqq));

    cfq_service_tree_add(cfqd, cfqq, 1);

    cfqq->slice_end = 0;
    cfq_mark_cfqq_slice_new(cfqq);
}

/*
 * Called when a new fs request (rq) is added (to cfqq). Check if there's
 * something we should do about it
 */
static void
cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
        struct request *rq)
{
    struct cfq_io_cq *cic = RQ_CIC(rq);

    cfqd->rq_queued++;
    if (rq->cmd_flags & REQ_PRIO)
        cfqq->prio_pending++;

    cfq_update_io_thinktime(cfqd, cfqq, cic);
    cfq_update_io_seektime(cfqd, cfqq, rq);
    cfq_update_idle_window(cfqd, cfqq, cic);

    cfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);

    if (cfqq == cfqd->active_queue) {
        /*
         * Remember that we saw a request from this process, but
         * don't start queuing just yet. Otherwise we risk seeing lots
         * of tiny requests, because we disrupt the normal plugging
         * and merging. If the request is already larger than a single
         * page, let it rip immediately. For that case we assume that
         * merging is already done. Ditto for a busy system that
         * has other work pending, don't risk delaying until the
         * idle timer unplug to continue working.
         */
        if (cfq_cfqq_wait_request(cfqq)) {
            if (blk_rq_bytes(rq) > PAGE_CACHE_SIZE ||
                cfqd->busy_queues > 1) {
                cfq_del_timer(cfqd, cfqq);
                cfq_clear_cfqq_wait_request(cfqq);
                __blk_run_queue(cfqd->queue);
            } else {
                cfqg_stats_update_idle_time(cfqq->cfqg);
                cfq_mark_cfqq_must_dispatch(cfqq);
            }
        }
    } else if (cfq_should_preempt(cfqd, cfqq, rq)) {
        /*
         * not the active queue - expire current slice if it is
         * idle and has expired it's mean thinktime or this new queue
         * has some old slice time left and is of higher priority or
         * this new queue is RT and the current one is BE
         */
        cfq_preempt_queue(cfqd, cfqq);
        __blk_run_queue(cfqd->queue);
    }
}

static void cfq_insert_request(struct request_queue *q, struct request *rq)
{
    struct cfq_data *cfqd = q->elevator->elevator_data;
    struct cfq_queue *cfqq = RQ_CFQQ(rq);

    cfq_log_cfqq(cfqd, cfqq, "insert_request");
    cfq_init_prio_data(cfqq, RQ_CIC(rq));

    rq_set_fifo_time(rq, jiffies + cfqd->cfq_fifo_expire[rq_is_sync(rq)]);
    list_add_tail(&rq->queuelist, &cfqq->fifo);
    cfq_add_rq_rb(rq);
    cfqg_stats_update_io_add(RQ_CFQG(rq), cfqd->serving_group,
                 rq->cmd_flags);
    cfq_rq_enqueued(cfqd, cfqq, rq);
}

/*
 * Update hw_tag based on peak queue depth over 50 samples under
 * sufficient load.
 */
static void cfq_update_hw_tag(struct cfq_data *cfqd)
{
    struct cfq_queue *cfqq = cfqd->active_queue;

    if (cfqd->rq_in_driver > cfqd->hw_tag_est_depth)
        cfqd->hw_tag_est_depth = cfqd->rq_in_driver;

    if (cfqd->hw_tag == 1)
        return;

    if (cfqd->rq_queued <= CFQ_HW_QUEUE_MIN &&
        cfqd->rq_in_driver <= CFQ_HW_QUEUE_MIN)
        return;

    /*
     * If active queue hasn't enough requests and can idle, cfq might not
     * dispatch sufficient requests to hardware. Don't zero hw_tag in this
     * case
     */
    if (cfqq && cfq_cfqq_idle_window(cfqq) &&
        cfqq->dispatched + cfqq->queued[0] + cfqq->queued[1] <
        CFQ_HW_QUEUE_MIN && cfqd->rq_in_driver < CFQ_HW_QUEUE_MIN)
        return;

    if (cfqd->hw_tag_samples++ < 50)
        return;

    if (cfqd->hw_tag_est_depth >= CFQ_HW_QUEUE_MIN)
        cfqd->hw_tag = 1;
    else
        cfqd->hw_tag = 0;
}

static bool cfq_should_wait_busy(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
    struct cfq_io_cq *cic = cfqd->active_cic;

    /* If the queue already has requests, don't wait */
    if (!RB_EMPTY_ROOT(&cfqq->sort_list))
        return false;

    /* If there are other queues in the group, don't wait */
    if (cfqq->cfqg->nr_cfqq > 1)
        return false;

    /* the only queue in the group, but think time is big */
    if (cfq_io_thinktime_big(cfqd, &cfqq->cfqg->ttime, true))
        return false;

    if (cfq_slice_used(cfqq))
        return true;

    /* if slice left is less than think time, wait busy */
    if (cic && sample_valid(cic->ttime.ttime_samples)
        && (cfqq->slice_end - jiffies < cic->ttime.ttime_mean))
        return true;

    /*
     * If think times is less than a jiffy than ttime_mean=0 and above
     * will not be true. It might happen that slice has not expired yet
     * but will expire soon (4-5 ns) during select_queue(). To cover the
     * case where think time is less than a jiffy, mark the queue wait
     * busy if only 1 jiffy is left in the slice.
     */
    if (cfqq->slice_end - jiffies == 1)
        return true;

    return false;
}

static void cfq_completed_request(struct request_queue *q, struct request *rq)
{
    struct cfq_queue *cfqq = RQ_CFQQ(rq);
    struct cfq_data *cfqd = cfqq->cfqd;
    const int sync = rq_is_sync(rq);
    unsigned long now;

    now = jiffies;
    cfq_log_cfqq(cfqd, cfqq, "complete rqnoidle %d",
             !!(rq->cmd_flags & REQ_NOIDLE));

    cfq_update_hw_tag(cfqd);

    WARN_ON(!cfqd->rq_in_driver);
    WARN_ON(!cfqq->dispatched);
    cfqd->rq_in_driver--;
    cfqq->dispatched--;
    (RQ_CFQG(rq))->dispatched--;
    cfqg_stats_update_completion(cfqq->cfqg, rq_start_time_ns(rq),
                     rq_io_start_time_ns(rq), rq->cmd_flags);

    cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]--;

    if (sync) {
        struct cfq_rb_root *service_tree;

        RQ_CIC(rq)->ttime.last_end_request = now;

        if (cfq_cfqq_on_rr(cfqq))
            service_tree = cfqq->service_tree;
        else
            service_tree = service_tree_for(cfqq->cfqg,
                cfqq_prio(cfqq), cfqq_type(cfqq));
        service_tree->ttime.last_end_request = now;
        if (!time_after(rq->start_time + cfqd->cfq_fifo_expire[1], now))
            cfqd->last_delayed_sync = now;
    }

#ifdef CONFIG_CFQ_GROUP_IOSCHED
    cfqq->cfqg->ttime.last_end_request = now;
#endif

    /*
     * If this is the active queue, check if it needs to be expired,
     * or if we want to idle in case it has no pending requests.
     */
    if (cfqd->active_queue == cfqq) {
        const bool cfqq_empty = RB_EMPTY_ROOT(&cfqq->sort_list);

        if (cfq_cfqq_slice_new(cfqq)) {
            cfq_set_prio_slice(cfqd, cfqq);
            cfq_clear_cfqq_slice_new(cfqq);
        }

        /*
         * Should we wait for next request to come in before we expire
         * the queue.
         */
        if (cfq_should_wait_busy(cfqd, cfqq)) {
            unsigned long extend_sl = cfqd->cfq_slice_idle;
            if (!cfqd->cfq_slice_idle)
                extend_sl = cfqd->cfq_group_idle;
            cfqq->slice_end = jiffies + extend_sl;
            cfq_mark_cfqq_wait_busy(cfqq);
            cfq_log_cfqq(cfqd, cfqq, "will busy wait");
        }

        /*
         * Idling is not enabled on:
         * - expired queues
         * - idle-priority queues
         * - async queues
         * - queues with still some requests queued
         * - when there is a close cooperator
         */
        if (cfq_slice_used(cfqq) || cfq_class_idle(cfqq))
            cfq_slice_expired(cfqd, 1);
        else if (sync && cfqq_empty &&
             !cfq_close_cooperator(cfqd, cfqq)) {
            cfq_arm_slice_timer(cfqd);
        }
    }

    if (!cfqd->rq_in_driver)
        cfq_schedule_dispatch(cfqd);
}

static inline int __cfq_may_queue(struct cfq_queue *cfqq)
{
    if (cfq_cfqq_wait_request(cfqq) && !cfq_cfqq_must_alloc_slice(cfqq)) {
        cfq_mark_cfqq_must_alloc_slice(cfqq);
        return ELV_MQUEUE_MUST;
    }

    return ELV_MQUEUE_MAY;
}

static int cfq_may_queue(struct request_queue *q, int rw)
{
    struct cfq_data *cfqd = q->elevator->elevator_data;
    struct task_struct *tsk = current;
    struct cfq_io_cq *cic;
    struct cfq_queue *cfqq;

    /*
     * don't force setup of a queue from here, as a call to may_queue
     * does not necessarily imply that a request actually will be queued.
     * so just lookup a possibly existing queue, or return 'may queue'
     * if that fails
     */
    cic = cfq_cic_lookup(cfqd, tsk->io_context);
    if (!cic)
        return ELV_MQUEUE_MAY;

    cfqq = cic_to_cfqq(cic, rw_is_sync(rw));
    if (cfqq) {
        cfq_init_prio_data(cfqq, cic);

        return __cfq_may_queue(cfqq);
    }

    return ELV_MQUEUE_MAY;
}

/*
 * queue lock held here
 */
static void cfq_put_request(struct request *rq)
{
    struct cfq_queue *cfqq = RQ_CFQQ(rq);

    if (cfqq) {
        const int rw = rq_data_dir(rq);

        BUG_ON(!cfqq->allocated[rw]);
        cfqq->allocated[rw]--;

        /* Put down rq reference on cfqg */
        cfqg_put(RQ_CFQG(rq));
        rq->elv.priv[0] = NULL;
        rq->elv.priv[1] = NULL;

        cfq_put_queue(cfqq);
    }
}

static struct cfq_queue *
cfq_merge_cfqqs(struct cfq_data *cfqd, struct cfq_io_cq *cic,
        struct cfq_queue *cfqq)
{
    cfq_log_cfqq(cfqd, cfqq, "merging with queue %p", cfqq->new_cfqq);
    cic_set_cfqq(cic, cfqq->new_cfqq, 1);
    cfq_mark_cfqq_coop(cfqq->new_cfqq);
    cfq_put_queue(cfqq);
    return cic_to_cfqq(cic, 1);
}

/*
 * Returns NULL if a new cfqq should be allocated, or the old cfqq if this
 * was the last process referring to said cfqq.
 */
static struct cfq_queue *
split_cfqq(struct cfq_io_cq *cic, struct cfq_queue *cfqq)
{
    if (cfqq_process_refs(cfqq) == 1) {
        cfqq->pid = current->pid;
        cfq_clear_cfqq_coop(cfqq);
        cfq_clear_cfqq_split_coop(cfqq);
        return cfqq;
    }

    cic_set_cfqq(cic, NULL, 1);

    cfq_put_cooperator(cfqq);

    cfq_put_queue(cfqq);
    return NULL;
}
/*
 * Allocate cfq data structures associated with this request.
 */
static int
cfq_set_request(struct request_queue *q, struct request *rq, struct bio *bio,
        gfp_t gfp_mask)
{
    struct cfq_data *cfqd = q->elevator->elevator_data;
    struct cfq_io_cq *cic = icq_to_cic(rq->elv.icq);
    const int rw = rq_data_dir(rq);
    const bool is_sync = rq_is_sync(rq);
    struct cfq_queue *cfqq;

    might_sleep_if(gfp_mask & __GFP_WAIT);

    spin_lock_irq(q->queue_lock);

    check_ioprio_changed(cic, bio);
    check_blkcg_changed(cic, bio);
new_queue:
    cfqq = cic_to_cfqq(cic, is_sync);
    if (!cfqq || cfqq == &cfqd->oom_cfqq) {
        cfqq = cfq_get_queue(cfqd, is_sync, cic, bio, gfp_mask);
        cic_set_cfqq(cic, cfqq, is_sync);
    } else {
        /*
         * If the queue was seeky for too long, break it apart.
         */
        if (cfq_cfqq_coop(cfqq) && cfq_cfqq_split_coop(cfqq)) {
            cfq_log_cfqq(cfqd, cfqq, "breaking apart cfqq");
            cfqq = split_cfqq(cic, cfqq);
            if (!cfqq)
                goto new_queue;
        }

        /*
         * Check to see if this queue is scheduled to merge with
         * another, closely cooperating queue.  The merging of
         * queues happens here as it must be done in process context.
         * The reference on new_cfqq was taken in merge_cfqqs.
         */
        if (cfqq->new_cfqq)
            cfqq = cfq_merge_cfqqs(cfqd, cic, cfqq);
    }

    cfqq->allocated[rw]++;

    cfqq->ref++;
    cfqg_get(cfqq->cfqg);
    rq->elv.priv[0] = cfqq;
    rq->elv.priv[1] = cfqq->cfqg;
    spin_unlock_irq(q->queue_lock);
    return 0;
}

static void cfq_kick_queue(struct work_struct *work)
{
    struct cfq_data *cfqd =
        container_of(work, struct cfq_data, unplug_work);
    struct request_queue *q = cfqd->queue;

    spin_lock_irq(q->queue_lock);
    __blk_run_queue(cfqd->queue);
    spin_unlock_irq(q->queue_lock);
}

/*
 * Timer running if the active_queue is currently idling inside its time slice
 */
static void cfq_idle_slice_timer(unsigned long data)
{
    struct cfq_data *cfqd = (struct cfq_data *) data;
    struct cfq_queue *cfqq;
    unsigned long flags;
    int timed_out = 1;

    cfq_log(cfqd, "idle timer fired");

    spin_lock_irqsave(cfqd->queue->queue_lock, flags);

    cfqq = cfqd->active_queue;
    if (cfqq) {
        timed_out = 0;

        /*
         * We saw a request before the queue expired, let it through
         */
        if (cfq_cfqq_must_dispatch(cfqq))
            goto out_kick;

        /*
         * expired
         */
        if (cfq_slice_used(cfqq))
            goto expire;

        /*
         * only expire and reinvoke request handler, if there are
         * other queues with pending requests
         */
        if (!cfqd->busy_queues)
            goto out_cont;

        /*
         * not expired and it has a request pending, let it dispatch
         */
        if (!RB_EMPTY_ROOT(&cfqq->sort_list))
            goto out_kick;

        /*
         * Queue depth flag is reset only when the idle didn't succeed
         */
        cfq_clear_cfqq_deep(cfqq);
    }
expire:
    cfq_slice_expired(cfqd, timed_out);
out_kick:
    cfq_schedule_dispatch(cfqd);
out_cont:
    spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
}

static void cfq_shutdown_timer_wq(struct cfq_data *cfqd)
{
    del_timer_sync(&cfqd->idle_slice_timer);
    cancel_work_sync(&cfqd->unplug_work);
}

static void cfq_put_async_queues(struct cfq_data *cfqd)
{
    int i;

    for (i = 0; i < IOPRIO_BE_NR; i++) {
        if (cfqd->async_cfqq[0][i])
            cfq_put_queue(cfqd->async_cfqq[0][i]);
        if (cfqd->async_cfqq[1][i])
            cfq_put_queue(cfqd->async_cfqq[1][i]);
    }

    if (cfqd->async_idle_cfqq)
        cfq_put_queue(cfqd->async_idle_cfqq);
}

static void cfq_exit_queue(struct elevator_queue *e)
{
    struct cfq_data *cfqd = e->elevator_data;
    struct request_queue *q = cfqd->queue;

    cfq_shutdown_timer_wq(cfqd);

    spin_lock_irq(q->queue_lock);

    if (cfqd->active_queue)
        __cfq_slice_expired(cfqd, cfqd->active_queue, 0);

    cfq_put_async_queues(cfqd);

    spin_unlock_irq(q->queue_lock);

    cfq_shutdown_timer_wq(cfqd);

#ifdef CONFIG_CFQ_GROUP_IOSCHED
    blkcg_deactivate_policy(q, &blkcg_policy_cfq);
#else
    kfree(cfqd->root_group);
#endif
    kfree(cfqd);
}

static int cfq_init_queue(struct request_queue *q)
{
    struct cfq_data *cfqd;
    struct blkcg_gq *blkg __maybe_unused;
    int i, ret;

    cfqd = kmalloc_node(sizeof(*cfqd), GFP_KERNEL | __GFP_ZERO, q->node);
    if (!cfqd)
        return -ENOMEM;

    cfqd->queue = q;
    q->elevator->elevator_data = cfqd;

    /* Init root service tree */
    cfqd->grp_service_tree = CFQ_RB_ROOT;

    /* Init root group and prefer root group over other groups by default */
#ifdef CONFIG_CFQ_GROUP_IOSCHED
    ret = blkcg_activate_policy(q, &blkcg_policy_cfq);
    if (ret)
        goto out_free;

    cfqd->root_group = blkg_to_cfqg(q->root_blkg);
#else
    ret = -ENOMEM;
    cfqd->root_group = kzalloc_node(sizeof(*cfqd->root_group),
                    GFP_KERNEL, cfqd->queue->node);
    if (!cfqd->root_group)
        goto out_free;

    cfq_init_cfqg_base(cfqd->root_group);
#endif
    cfqd->root_group->weight = 2 * CFQ_WEIGHT_DEFAULT;

    /*
     * Not strictly needed (since RB_ROOT just clears the node and we
     * zeroed cfqd on alloc), but better be safe in case someone decides
     * to add magic to the rb code
     */
    for (i = 0; i < CFQ_PRIO_LISTS; i++)
        cfqd->prio_trees[i] = RB_ROOT;

    /*
     * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues.
     * Grab a permanent reference to it, so that the normal code flow
     * will not attempt to free it.  oom_cfqq is linked to root_group
     * but shouldn't hold a reference as it'll never be unlinked.  Lose
     * the reference from linking right away.
     */
    cfq_init_cfqq(cfqd, &cfqd->oom_cfqq, 1, 0);
    cfqd->oom_cfqq.ref++;

    spin_lock_irq(q->queue_lock);
    cfq_link_cfqq_cfqg(&cfqd->oom_cfqq, cfqd->root_group);
    cfqg_put(cfqd->root_group);
    spin_unlock_irq(q->queue_lock);

    init_timer(&cfqd->idle_slice_timer);
    cfqd->idle_slice_timer.function = cfq_idle_slice_timer;
    cfqd->idle_slice_timer.data = (unsigned long) cfqd;

    INIT_WORK(&cfqd->unplug_work, cfq_kick_queue);

    cfqd->cfq_quantum = cfq_quantum;
    cfqd->cfq_fifo_expire[0] = cfq_fifo_expire[0];
    cfqd->cfq_fifo_expire[1] = cfq_fifo_expire[1];
    cfqd->cfq_back_max = cfq_back_max;
    cfqd->cfq_back_penalty = cfq_back_penalty;
    cfqd->cfq_slice[0] = cfq_slice_async;
    cfqd->cfq_slice[1] = cfq_slice_sync;
    cfqd->cfq_target_latency = cfq_target_latency;
    cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
    cfqd->cfq_slice_idle = cfq_slice_idle;
    cfqd->cfq_group_idle = cfq_group_idle;
    cfqd->cfq_latency = 1;
    cfqd->hw_tag = -1;
    /*
     * we optimistically start assuming sync ops weren't delayed in last
     * second, in order to have larger depth for async operations.
     */
    cfqd->last_delayed_sync = jiffies - HZ;
    return 0;

out_free:
    kfree(cfqd);
    return ret;
}

/*
 * sysfs parts below -->
 */
static ssize_t
cfq_var_show(unsigned int var, char *page)
{
    return sprintf(page, "%d\n", var);
}

static ssize_t
cfq_var_store(unsigned int *var, const char *page, size_t count)
{
    char *p = (char *) page;

    *var = simple_strtoul(p, &p, 10);
    return count;
}

#define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                \
static ssize_t __FUNC(struct elevator_queue *e, char *page)     \
{                                   \
    struct cfq_data *cfqd = e->elevator_data;           \
    unsigned int __data = __VAR;                    \
    if (__CONV)                         \
        __data = jiffies_to_msecs(__data);          \
    return cfq_var_show(__data, (page));                \
}
SHOW_FUNCTION(cfq_quantum_show, cfqd->cfq_quantum, 0);
SHOW_FUNCTION(cfq_fifo_expire_sync_show, cfqd->cfq_fifo_expire[1], 1);
SHOW_FUNCTION(cfq_fifo_expire_async_show, cfqd->cfq_fifo_expire[0], 1);
SHOW_FUNCTION(cfq_back_seek_max_show, cfqd->cfq_back_max, 0);
SHOW_FUNCTION(cfq_back_seek_penalty_show, cfqd->cfq_back_penalty, 0);
SHOW_FUNCTION(cfq_slice_idle_show, cfqd->cfq_slice_idle, 1);
SHOW_FUNCTION(cfq_group_idle_show, cfqd->cfq_group_idle, 1);
SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
SHOW_FUNCTION(cfq_low_latency_show, cfqd->cfq_latency, 0);
SHOW_FUNCTION(cfq_target_latency_show, cfqd->cfq_target_latency, 1);
#undef SHOW_FUNCTION

#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)         \
static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
{                                   \
    struct cfq_data *cfqd = e->elevator_data;           \
    unsigned int __data;                        \
    int ret = cfq_var_store(&__data, (page), count);        \
    if (__data < (MIN))                     \
        __data = (MIN);                     \
    else if (__data > (MAX))                    \
        __data = (MAX);                     \
    if (__CONV)                         \
        *(__PTR) = msecs_to_jiffies(__data);            \
    else                                \
        *(__PTR) = __data;                  \
    return ret;                         \
}
STORE_FUNCTION(cfq_quantum_store, &cfqd->cfq_quantum, 1, UINT_MAX, 0);
STORE_FUNCTION(cfq_fifo_expire_sync_store, &cfqd->cfq_fifo_expire[1], 1,
        UINT_MAX, 1);
STORE_FUNCTION(cfq_fifo_expire_async_store, &cfqd->cfq_fifo_expire[0], 1,
        UINT_MAX, 1);
STORE_FUNCTION(cfq_back_seek_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
STORE_FUNCTION(cfq_back_seek_penalty_store, &cfqd->cfq_back_penalty, 1,
        UINT_MAX, 0);
STORE_FUNCTION(cfq_slice_idle_store, &cfqd->cfq_slice_idle, 0, UINT_MAX, 1);
STORE_FUNCTION(cfq_group_idle_store, &cfqd->cfq_group_idle, 0, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1,
        UINT_MAX, 0);
STORE_FUNCTION(cfq_low_latency_store, &cfqd->cfq_latency, 0, 1, 0);
STORE_FUNCTION(cfq_target_latency_store, &cfqd->cfq_target_latency, 1, UINT_MAX, 1);
#undef STORE_FUNCTION

#define CFQ_ATTR(name) \
    __ATTR(name, S_IRUGO|S_IWUSR, cfq_##name##_show, cfq_##name##_store)

static struct elv_fs_entry cfq_attrs[] = {
    CFQ_ATTR(quantum),
    CFQ_ATTR(fifo_expire_sync),
    CFQ_ATTR(fifo_expire_async),
    CFQ_ATTR(back_seek_max),
    CFQ_ATTR(back_seek_penalty),
    CFQ_ATTR(slice_sync),
    CFQ_ATTR(slice_async),
    CFQ_ATTR(slice_async_rq),
    CFQ_ATTR(slice_idle),
    CFQ_ATTR(group_idle),
    CFQ_ATTR(low_latency),
    CFQ_ATTR(target_latency),
    __ATTR_NULL
};

static struct elevator_type iosched_cfq = {
    .ops = {
        .elevator_merge_fn =        cfq_merge,
        .elevator_merged_fn =       cfq_merged_request,
        .elevator_merge_req_fn =    cfq_merged_requests,
        .elevator_allow_merge_fn =  cfq_allow_merge,
        .elevator_bio_merged_fn =   cfq_bio_merged,
        .elevator_dispatch_fn =     cfq_dispatch_requests,
        .elevator_add_req_fn =      cfq_insert_request,
        .elevator_activate_req_fn = cfq_activate_request,
        .elevator_deactivate_req_fn =   cfq_deactivate_request,
        .elevator_completed_req_fn =    cfq_completed_request,
        .elevator_former_req_fn =   elv_rb_former_request,
        .elevator_latter_req_fn =   elv_rb_latter_request,
        .elevator_init_icq_fn =     cfq_init_icq,
        .elevator_exit_icq_fn =     cfq_exit_icq,
        .elevator_set_req_fn =      cfq_set_request,
        .elevator_put_req_fn =      cfq_put_request,
        .elevator_may_queue_fn =    cfq_may_queue,
        .elevator_init_fn =     cfq_init_queue,
        .elevator_exit_fn =     cfq_exit_queue,
    },
    .icq_size   =   sizeof(struct cfq_io_cq),
    .icq_align  =   __alignof__(struct cfq_io_cq),
    .elevator_attrs =   cfq_attrs,
    .elevator_name  =   "cfq",
    .elevator_owner =   THIS_MODULE,
};

#ifdef CONFIG_CFQ_GROUP_IOSCHED
static struct blkcg_policy blkcg_policy_cfq = {
    .pd_size        = sizeof(struct cfq_group),
    .cftypes        = cfq_blkcg_files,

    .pd_init_fn     = cfq_pd_init,
    .pd_reset_stats_fn  = cfq_pd_reset_stats,
};
#endif

static int __init cfq_init(void)
{
    int ret;

    /*
     * could be 0 on HZ < 1000 setups
     */
    if (!cfq_slice_async)
        cfq_slice_async = 1;
    if (!cfq_slice_idle)
        cfq_slice_idle = 1;

#ifdef CONFIG_CFQ_GROUP_IOSCHED
    if (!cfq_group_idle)
        cfq_group_idle = 1;

    ret = blkcg_policy_register(&blkcg_policy_cfq);
    if (ret)
        return ret;
#else
    cfq_group_idle = 0;
#endif

    ret = -ENOMEM;
    cfq_pool = KMEM_CACHE(cfq_queue, 0);
    if (!cfq_pool)
        goto err_pol_unreg;

    ret = elv_register(&iosched_cfq);
    if (ret)
        goto err_free_pool;

    return 0;

err_free_pool:
    kmem_cache_destroy(cfq_pool);
err_pol_unreg:
#ifdef CONFIG_CFQ_GROUP_IOSCHED
    blkcg_policy_unregister(&blkcg_policy_cfq);
#endif
    return ret;
}

static void __exit cfq_exit(void)
{
#ifdef CONFIG_CFQ_GROUP_IOSCHED
    blkcg_policy_unregister(&blkcg_policy_cfq);
#endif
    elv_unregister(&iosched_cfq);
    kmem_cache_destroy(cfq_pool);
}

module_init(cfq_init);
module_exit(cfq_exit);

MODULE_AUTHOR("Jens Axboe");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Completely Fair Queueing IO scheduler");