blk-iopoll.c

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/*
 * Functions related to interrupt-poll handling in the block layer. This
 * is similar to NAPI for network devices.
 */
#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/blk-iopoll.h>
#include <linux/delay.h>

#include "blk.h"

int blk_iopoll_enabled = 1;
EXPORT_SYMBOL(blk_iopoll_enabled);

static unsigned int blk_iopoll_budget __read_mostly = 256;

static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);

void blk_iopoll_sched(struct blk_iopoll *iop)
{
    unsigned long flags;

    local_irq_save(flags);
    list_add_tail(&iop->list, &__get_cpu_var(blk_cpu_iopoll));
    __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
    local_irq_restore(flags);
}
EXPORT_SYMBOL(blk_iopoll_sched);

void __blk_iopoll_complete(struct blk_iopoll *iop)
{
    list_del(&iop->list);
    smp_mb__before_clear_bit();
    clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
}
EXPORT_SYMBOL(__blk_iopoll_complete);

void blk_iopoll_complete(struct blk_iopoll *iopoll)
{
    unsigned long flags;

    local_irq_save(flags);
    __blk_iopoll_complete(iopoll);
    local_irq_restore(flags);
}
EXPORT_SYMBOL(blk_iopoll_complete);

static void blk_iopoll_softirq(struct softirq_action *h)
{
    struct list_head *list = &__get_cpu_var(blk_cpu_iopoll);
    int rearm = 0, budget = blk_iopoll_budget;
    unsigned long start_time = jiffies;

    local_irq_disable();

    while (!list_empty(list)) {
        struct blk_iopoll *iop;
        int work, weight;

        /*
         * If softirq window is exhausted then punt.
         */
        if (budget <= 0 || time_after(jiffies, start_time)) {
            rearm = 1;
            break;
        }

        local_irq_enable();

        /* Even though interrupts have been re-enabled, this
         * access is safe because interrupts can only add new
         * entries to the tail of this list, and only ->poll()
         * calls can remove this head entry from the list.
         */
        iop = list_entry(list->next, struct blk_iopoll, list);

        weight = iop->weight;
        work = 0;
        if (test_bit(IOPOLL_F_SCHED, &iop->state))
            work = iop->poll(iop, weight);

        budget -= work;

        local_irq_disable();

        /*
         * Drivers must not modify the iopoll state, if they
         * consume their assigned weight (or more, some drivers can't
         * easily just stop processing, they have to complete an
         * entire mask of commands).In such cases this code
         * still "owns" the iopoll instance and therefore can
         * move the instance around on the list at-will.
         */
        if (work >= weight) {
            if (blk_iopoll_disable_pending(iop))
                __blk_iopoll_complete(iop);
            else
                list_move_tail(&iop->list, list);
        }
    }

    if (rearm)
        __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);

    local_irq_enable();
}

void blk_iopoll_disable(struct blk_iopoll *iop)
{
    set_bit(IOPOLL_F_DISABLE, &iop->state);
    while (test_and_set_bit(IOPOLL_F_SCHED, &iop->state))
        msleep(1);
    clear_bit(IOPOLL_F_DISABLE, &iop->state);
}
EXPORT_SYMBOL(blk_iopoll_disable);

void blk_iopoll_enable(struct blk_iopoll *iop)
{
    BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
    smp_mb__before_clear_bit();
    clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
}
EXPORT_SYMBOL(blk_iopoll_enable);

void blk_iopoll_init(struct blk_iopoll *iop, int weight, blk_iopoll_fn *poll_fn)
{
    memset(iop, 0, sizeof(*iop));
    INIT_LIST_HEAD(&iop->list);
    iop->weight = weight;
    iop->poll = poll_fn;
    set_bit(IOPOLL_F_SCHED, &iop->state);
}
EXPORT_SYMBOL(blk_iopoll_init);

static int __cpuinit blk_iopoll_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_iopoll, cpu),
                 &__get_cpu_var(blk_cpu_iopoll));
        __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
        local_irq_enable();
    }

    return NOTIFY_OK;
}

static struct notifier_block __cpuinitdata blk_iopoll_cpu_notifier = {
    .notifier_call  = blk_iopoll_cpu_notify,
};

static __init int blk_iopoll_setup(void)
{
    int i;

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

    open_softirq(BLOCK_IOPOLL_SOFTIRQ, blk_iopoll_softirq);
    register_hotcpu_notifier(&blk_iopoll_cpu_notifier);
    return 0;
}
subsys_initcall(blk_iopoll_setup);