block/blk-softirq.c

   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
  14 static 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  */
  20 static 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)
  39 static 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  */
  58 static 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, 0);
  68                 return 0;
  69         }
  70
  71         return 1;
  72 }
  73 #else /* CONFIG_SMP && CONFIG_USE_GENERIC_SMP_HELPERS */
  74 static int raise_blk_irq(int cpu, struct request *rq)
  75 {
  76         return 1;
  77 }
  78 #endif
  79
  80 static 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
 100 static struct notifier_block __cpuinitdata blk_cpu_notifier = {
 101         .notifier_call  = blk_cpu_notify,
 102 };
 103
 104 void __blk_complete_request(struct request *req)
 105 {
 106         int ccpu, cpu, group_cpu = NR_CPUS;
 107         struct request_queue *q = req->q;
 108         unsigned long flags;
 109
 110         BUG_ON(!q->softirq_done_fn);
 111
 112         local_irq_save(flags);
 113         cpu = smp_processor_id();
 114
 115         /*
 116          * Select completion CPU
 117          */
 118         if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) && req->cpu != -1) {
 119                 ccpu = req->cpu;
 120                 if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags)) {
 121                         ccpu = blk_cpu_to_group(ccpu);
 122                         group_cpu = blk_cpu_to_group(cpu);
 123                 }
 124         } else
 125                 ccpu = cpu;
 126
 127         /*
 128          * If current CPU and requested CPU are in the same group, running
 129          * softirq in current CPU. One might concern this is just like
 130          * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
 131          * running in interrupt handler, and currently I/O controller doesn't
 132          * support multiple interrupts, so current CPU is unique actually. This
 133          * avoids IPI sending from current CPU to the first CPU of a group.
 134          */
 135         if (ccpu == cpu || ccpu == group_cpu) {
 136                 struct list_head *list;
 137 do_local:
 138                 list = &__get_cpu_var(blk_cpu_done);
 139                 list_add_tail(&req->csd.list, list);
 140
 141                 /*
 142                  * if the list only contains our just added request,
 143                  * signal a raise of the softirq. If there are already
 144                  * entries there, someone already raised the irq but it
 145                  * hasn't run yet.
 146                  */
 147                 if (list->next == &req->csd.list)
 148                         raise_softirq_irqoff(BLOCK_SOFTIRQ);
 149         } else if (raise_blk_irq(ccpu, req))
 150                 goto do_local;
 151
 152         local_irq_restore(flags);
 153 }
 154
 155 /**
 156  * blk_complete_request - end I/O on a request
 157  * @req:      the request being processed
 158  *
 159  * Description:
 160  *     Ends all I/O on a request. It does not handle partial completions,
 161  *     unless the driver actually implements this in its completion callback
 162  *     through requeueing. The actual completion happens out-of-order,
 163  *     through a softirq handler. The user must have registered a completion
 164  *     callback through blk_queue_softirq_done().
 165  **/
 166 void blk_complete_request(struct request *req)
 167 {
 168         if (unlikely(blk_should_fake_timeout(req->q)))
 169                 return;
 170         if (!blk_mark_rq_complete(req))
 171                 __blk_complete_request(req);
 172 }
 173 EXPORT_SYMBOL(blk_complete_request);
 174
 175 static __init int blk_softirq_init(void)
 176 {
 177         int i;
 178
 179         for_each_possible_cpu(i)
 180                 INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
 181
 182         open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 183         register_hotcpu_notifier(&blk_cpu_notifier);
 184         return 0;
 185 }
 186 subsys_initcall(blk_softirq_init);