linux/block/blk-softirq.c
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   1/*
   2 * Functions related to softirq rq completions
   3 */
   4#include <linux/kernel.h>
   5#include <linux/module.h>
   6#include <linux/init.h>
   7#include <linux/bio.h>
   8#include <linux/blkdev.h>
   9#include <linux/interrupt.h>
  10#include <linux/cpu.h>
  11
  12#include "blk.h"
  13
  14static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
  15
  16/*
  17 * Softirq action handler - move entries to local list and loop over them
  18 * while passing them to the queue registered handler.
  19 */
  20static void blk_done_softirq(struct softirq_action *h)
  21{
  22        struct list_head *cpu_list, local_list;
  23
  24        local_irq_disable();
  25        cpu_list = &__get_cpu_var(blk_cpu_done);
  26        list_replace_init(cpu_list, &local_list);
  27        local_irq_enable();
  28
  29        while (!list_empty(&local_list)) {
  30                struct request *rq;
  31
  32                rq = list_entry(local_list.next, struct request, csd.list);
  33                list_del_init(&rq->csd.list);
  34                rq->q->softirq_done_fn(rq);
  35        }
  36}
  37
  38#if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)
  39static void trigger_softirq(void *data)
  40{
  41        struct request *rq = data;
  42        unsigned long flags;
  43        struct list_head *list;
  44
  45        local_irq_save(flags);
  46        list = &__get_cpu_var(blk_cpu_done);
  47        list_add_tail(&rq->csd.list, list);
  48
  49        if (list->next == &rq->csd.list)
  50                raise_softirq_irqoff(BLOCK_SOFTIRQ);
  51
  52        local_irq_restore(flags);
  53}
  54
  55/*
  56 * Setup and invoke a run of 'trigger_softirq' on the given cpu.
  57 */
  58static int raise_blk_irq(int cpu, struct request *rq)
  59{
  60        if (cpu_online(cpu)) {
  61                struct call_single_data *data = &rq->csd;
  62
  63                data->func = trigger_softirq;
  64                data->info = rq;
  65                data->flags = 0;
  66
  67                __smp_call_function_single(cpu, data);
  68                return 0;
  69        }
  70
  71        return 1;
  72}
  73#else /* CONFIG_SMP && CONFIG_USE_GENERIC_SMP_HELPERS */
  74static int raise_blk_irq(int cpu, struct request *rq)
  75{
  76        return 1;
  77}
  78#endif
  79
  80static int __cpuinit blk_cpu_notify(struct notifier_block *self,
  81                                    unsigned long action, void *hcpu)
  82{
  83        /*
  84         * If a CPU goes away, splice its entries to the current CPU
  85         * and trigger a run of the softirq
  86         */
  87        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
  88                int cpu = (unsigned long) hcpu;
  89
  90                local_irq_disable();
  91                list_splice_init(&per_cpu(blk_cpu_done, cpu),
  92                                 &__get_cpu_var(blk_cpu_done));
  93                raise_softirq_irqoff(BLOCK_SOFTIRQ);
  94                local_irq_enable();
  95        }
  96
  97        return NOTIFY_OK;
  98}
  99
 100static struct notifier_block __cpuinitdata blk_cpu_notifier = {
 101        .notifier_call  = blk_cpu_notify,
 102};
 103
 104void __blk_complete_request(struct request *req)
 105{
 106        struct request_queue *q = req->q;
 107        unsigned long flags;
 108        int ccpu, cpu, group_cpu;
 109
 110        BUG_ON(!q->softirq_done_fn);
 111
 112        local_irq_save(flags);
 113        cpu = smp_processor_id();
 114        group_cpu = blk_cpu_to_group(cpu);
 115
 116        /*
 117         * Select completion CPU
 118         */
 119        if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) && req->cpu != -1)
 120                ccpu = req->cpu;
 121        else
 122                ccpu = cpu;
 123
 124        if (ccpu == cpu || ccpu == group_cpu) {
 125                struct list_head *list;
 126do_local:
 127                list = &__get_cpu_var(blk_cpu_done);
 128                list_add_tail(&req->csd.list, list);
 129
 130                /*
 131                 * if the list only contains our just added request,
 132                 * signal a raise of the softirq. If there are already
 133                 * entries there, someone already raised the irq but it
 134                 * hasn't run yet.
 135                 */
 136                if (list->next == &req->csd.list)
 137                        raise_softirq_irqoff(BLOCK_SOFTIRQ);
 138        } else if (raise_blk_irq(ccpu, req))
 139                goto do_local;
 140
 141        local_irq_restore(flags);
 142}
 143
 144/**
 145 * blk_complete_request - end I/O on a request
 146 * @req:      the request being processed
 147 *
 148 * Description:
 149 *     Ends all I/O on a request. It does not handle partial completions,
 150 *     unless the driver actually implements this in its completion callback
 151 *     through requeueing. The actual completion happens out-of-order,
 152 *     through a softirq handler. The user must have registered a completion
 153 *     callback through blk_queue_softirq_done().
 154 **/
 155void blk_complete_request(struct request *req)
 156{
 157        if (unlikely(blk_should_fake_timeout(req->q)))
 158                return;
 159        if (!blk_mark_rq_complete(req))
 160                __blk_complete_request(req);
 161}
 162EXPORT_SYMBOL(blk_complete_request);
 163
 164__init int blk_softirq_init(void)
 165{
 166        int i;
 167
 168        for_each_possible_cpu(i)
 169                INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
 170
 171        open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 172        register_hotcpu_notifier(&blk_cpu_notifier);
 173        return 0;
 174}
 175subsys_initcall(blk_softirq_init);
 176