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TOMOYO Linux Cross Reference
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 #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, 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_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->ipi_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->ipi_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);
187 

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