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 #include <linux/sched.h>
  12
  13 #include "blk.h"
  14
  15 static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
  16
  17 /*
  18  * Softirq action handler - move entries to local list and loop over them
  19  * while passing them to the queue registered handler.
  20  */
  21 static void blk_done_softirq(struct softirq_action *h)
  22 {
  23         struct list_head *cpu_list, local_list;
  24
  25         local_irq_disable();
  26         cpu_list = this_cpu_ptr(&blk_cpu_done);
  27         list_replace_init(cpu_list, &local_list);
  28         local_irq_enable();
  29
  30         while (!list_empty(&local_list)) {
  31                 struct request *rq;
  32
  33                 rq = list_entry(local_list.next, struct request, csd.list);
  34                 list_del_init(&rq->csd.list);
  35                 rq->q->softirq_done_fn(rq);
  36         }
  37 }
  38
  39 #ifdef CONFIG_SMP
  40 static void trigger_softirq(void *data)
  41 {
  42         struct request *rq = data;
  43         unsigned long flags;
  44         struct list_head *list;
  45
  46         local_irq_save(flags);
  47         list = this_cpu_ptr(&blk_cpu_done);
  48         list_add_tail(&rq->csd.list, list);
  49
  50         if (list->next == &rq->csd.list)
  51                 raise_softirq_irqoff(BLOCK_SOFTIRQ);
  52
  53         local_irq_restore(flags);
  54 }
  55
  56 /*
  57  * Setup and invoke a run of 'trigger_softirq' on the given cpu.
  58  */
  59 static int raise_blk_irq(int cpu, struct request *rq)
  60 {
  61         if (cpu_online(cpu)) {
  62                 struct call_single_data *data = &rq->csd;
  63
  64                 data->func = trigger_softirq;
  65                 data->info = rq;
  66                 data->flags = 0;
  67
  68                 __smp_call_function_single(cpu, data, 0);
  69                 return 0;
  70         }
  71
  72         return 1;
  73 }
  74 #else /* CONFIG_SMP */
  75 static int raise_blk_irq(int cpu, struct request *rq)
  76 {
  77         return 1;
  78 }
  79 #endif
  80
  81 static int blk_cpu_notify(struct notifier_block *self, unsigned long action,
  82                           void *hcpu)
  83 {
  84         /*
  85          * If a CPU goes away, splice its entries to the current CPU
  86          * and trigger a run of the softirq
  87          */
  88         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
  89                 int cpu = (unsigned long) hcpu;
  90
  91                 local_irq_disable();
  92                 list_splice_init(&per_cpu(blk_cpu_done, cpu),
  93                                  this_cpu_ptr(&blk_cpu_done));
  94                 raise_softirq_irqoff(BLOCK_SOFTIRQ);
  95                 local_irq_enable();
  96         }
  97
  98         return NOTIFY_OK;
  99 }
 100
 101 static struct notifier_block blk_cpu_notifier = {
 102         .notifier_call  = blk_cpu_notify,
 103 };
 104
 105 void __blk_complete_request(struct request *req)
 106 {
 107         int ccpu, cpu;
 108         struct request_queue *q = req->q;
 109         unsigned long flags;
 110         bool shared = false;
 111
 112         BUG_ON(!q->softirq_done_fn);
 113
 114         local_irq_save(flags);
 115         cpu = smp_processor_id();
 116
 117         /*
 118          * Select completion CPU
 119          */
 120         if (req->cpu != -1) {
 121                 ccpu = req->cpu;
 122                 if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
 123                         shared = cpus_share_cache(cpu, ccpu);
 124         } else
 125                 ccpu = cpu;
 126
 127         /*
 128          * If current CPU and requested CPU share a cache, run the softirq on
 129          * the 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 || shared) {
 136                 struct list_head *list;
 137 do_local:
 138                 list = this_cpu_ptr(&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);