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 __latent_entropy 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, ipi_list);
  34                 list_del_init(&rq->ipi_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->ipi_list, list);
  49
  50         if (list->next == &rq->ipi_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_async(cpu, data);
  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_softirq_cpu_dead(unsigned int cpu)
  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         local_irq_disable();
  88         list_splice_init(&per_cpu(blk_cpu_done, cpu),
  89                          this_cpu_ptr(&blk_cpu_done));
  90         raise_softirq_irqoff(BLOCK_SOFTIRQ);
  91         local_irq_enable();
  92
  93         return 0;
  94 }
  95
  96 void __blk_complete_request(struct request *req)
  97 {
  98         int ccpu, cpu;
  99         struct request_queue *q = req->q;
 100         unsigned long flags;
 101         bool shared = false;
 102
 103         BUG_ON(!q->softirq_done_fn);
 104
 105         local_irq_save(flags);
 106         cpu = smp_processor_id();
 107
 108         /*
 109          * Select completion CPU
 110          */
 111         if (req->cpu != -1) {
 112                 ccpu = req->cpu;
 113                 if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
 114                         shared = cpus_share_cache(cpu, ccpu);
 115         } else
 116                 ccpu = cpu;
 117
 118         /*
 119          * If current CPU and requested CPU share a cache, run the softirq on
 120          * the current CPU. One might concern this is just like
 121          * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
 122          * running in interrupt handler, and currently I/O controller doesn't
 123          * support multiple interrupts, so current CPU is unique actually. This
 124          * avoids IPI sending from current CPU to the first CPU of a group.
 125          */
 126         if (ccpu == cpu || shared) {
 127                 struct list_head *list;
 128 do_local:
 129                 list = this_cpu_ptr(&blk_cpu_done);
 130                 list_add_tail(&req->ipi_list, list);
 131
 132                 /*
 133                  * if the list only contains our just added request,
 134                  * signal a raise of the softirq. If there are already
 135                  * entries there, someone already raised the irq but it
 136                  * hasn't run yet.
 137                  */
 138                 if (list->next == &req->ipi_list)
 139                         raise_softirq_irqoff(BLOCK_SOFTIRQ);
 140         } else if (raise_blk_irq(ccpu, req))
 141                 goto do_local;
 142
 143         local_irq_restore(flags);
 144 }
 145
 146 /**
 147  * blk_complete_request - end I/O on a request
 148  * @req:      the request being processed
 149  *
 150  * Description:
 151  *     Ends all I/O on a request. It does not handle partial completions,
 152  *     unless the driver actually implements this in its completion callback
 153  *     through requeueing. The actual completion happens out-of-order,
 154  *     through a softirq handler. The user must have registered a completion
 155  *     callback through blk_queue_softirq_done().
 156  **/
 157 void blk_complete_request(struct request *req)
 158 {
 159         if (unlikely(blk_should_fake_timeout(req->q)))
 160                 return;
 161         if (!blk_mark_rq_complete(req))
 162                 __blk_complete_request(req);
 163 }
 164 EXPORT_SYMBOL(blk_complete_request);
 165
 166 static __init int blk_softirq_init(void)
 167 {
 168         int i;
 169
 170         for_each_possible_cpu(i)
 171                 INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
 172
 173         open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 174         cpuhp_setup_state_nocalls(CPUHP_BLOCK_SOFTIRQ_DEAD,
 175                                   "block/softirq:dead", NULL,
 176                                   blk_softirq_cpu_dead);
 177         return 0;
 178 }
 179 subsys_initcall(blk_softirq_init);