blk-softirq.c

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/*
 * Functions related to softirq rq completions
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/interrupt.h>
#include <linux/cpu.h>
#include <linux/sched.h>

#include "blk.h"

static DEFINE_PER_CPU(struct list_head, blk_cpu_done);

/*
 * Softirq action handler - move entries to local list and loop over them
 * while passing them to the queue registered handler.
 */
static void blk_done_softirq(struct softirq_action *h)
{
    struct list_head *cpu_list, local_list;

    local_irq_disable();
    cpu_list = &__get_cpu_var(blk_cpu_done);
    list_replace_init(cpu_list, &local_list);
    local_irq_enable();

    while (!list_empty(&local_list)) {
        struct request *rq;

        rq = list_entry(local_list.next, struct request, csd.list);
        list_del_init(&rq->csd.list);
        rq->q->softirq_done_fn(rq);
    }
}

#if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)
static void trigger_softirq(void *data)
{
    struct request *rq = data;
    unsigned long flags;
    struct list_head *list;

    local_irq_save(flags);
    list = &__get_cpu_var(blk_cpu_done);
    list_add_tail(&rq->csd.list, list);

    if (list->next == &rq->csd.list)
        raise_softirq_irqoff(BLOCK_SOFTIRQ);

    local_irq_restore(flags);
}

/*
 * Setup and invoke a run of 'trigger_softirq' on the given cpu.
 */
static int raise_blk_irq(int cpu, struct request *rq)
{
    if (cpu_online(cpu)) {
        struct call_single_data *data = &rq->csd;

        data->func = trigger_softirq;
        data->info = rq;
        data->flags = 0;

        __smp_call_function_single(cpu, data, 0);
        return 0;
    }

    return 1;
}
#else /* CONFIG_SMP && CONFIG_USE_GENERIC_SMP_HELPERS */
static int raise_blk_irq(int cpu, struct request *rq)
{
    return 1;
}
#endif

static int __cpuinit blk_cpu_notify(struct notifier_block *self,
                    unsigned long action, void *hcpu)
{
    /*
     * If a CPU goes away, splice its entries to the current CPU
     * and trigger a run of the softirq
     */
    if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
        int cpu = (unsigned long) hcpu;

        local_irq_disable();
        list_splice_init(&per_cpu(blk_cpu_done, cpu),
                 &__get_cpu_var(blk_cpu_done));
        raise_softirq_irqoff(BLOCK_SOFTIRQ);
        local_irq_enable();
    }

    return NOTIFY_OK;
}

static struct notifier_block __cpuinitdata blk_cpu_notifier = {
    .notifier_call  = blk_cpu_notify,
};

void __blk_complete_request(struct request *req)
{
    int ccpu, cpu;
    struct request_queue *q = req->q;
    unsigned long flags;
    bool shared = false;

    BUG_ON(!q->softirq_done_fn);

    local_irq_save(flags);
    cpu = smp_processor_id();

    /*
     * Select completion CPU
     */
    if (req->cpu != -1) {
        ccpu = req->cpu;
        if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
            shared = cpus_share_cache(cpu, ccpu);
    } else
        ccpu = cpu;

    /*
     * If current CPU and requested CPU share a cache, run the softirq on
     * the current CPU. One might concern this is just like
     * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
     * running in interrupt handler, and currently I/O controller doesn't
     * support multiple interrupts, so current CPU is unique actually. This
     * avoids IPI sending from current CPU to the first CPU of a group.
     */
    if (ccpu == cpu || shared) {
        struct list_head *list;
do_local:
        list = &__get_cpu_var(blk_cpu_done);
        list_add_tail(&req->csd.list, list);

        /*
         * if the list only contains our just added request,
         * signal a raise of the softirq. If there are already
         * entries there, someone already raised the irq but it
         * hasn't run yet.
         */
        if (list->next == &req->csd.list)
            raise_softirq_irqoff(BLOCK_SOFTIRQ);
    } else if (raise_blk_irq(ccpu, req))
        goto do_local;

    local_irq_restore(flags);
}

void blk_complete_request(struct request *req)
{
    if (unlikely(blk_should_fake_timeout(req->q)))
        return;
    if (!blk_mark_rq_complete(req))
        __blk_complete_request(req);
}
EXPORT_SYMBOL(blk_complete_request);

static __init int blk_softirq_init(void)
{
    int i;

    for_each_possible_cpu(i)
        INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));

    open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
    register_hotcpu_notifier(&blk_cpu_notifier);
    return 0;
}
subsys_initcall(blk_softirq_init);