Linux Kernel  3.7.1
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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 
26  cpu_list = &__get_cpu_var(blk_cpu_done);
27  list_replace_init(cpu_list, &local_list);
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 #if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)
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 = &__get_cpu_var(blk_cpu_done);
48  list_add_tail(&rq->csd.list, list);
49 
50  if (list->next == &rq->csd.list)
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 && CONFIG_USE_GENERIC_SMP_HELPERS */
75 static int raise_blk_irq(int cpu, struct request *rq)
76 {
77  return 1;
78 }
79 #endif
80 
81 static int __cpuinit blk_cpu_notify(struct notifier_block *self,
82  unsigned long action, 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 
92  list_splice_init(&per_cpu(blk_cpu_done, cpu),
93  &__get_cpu_var(blk_cpu_done));
96  }
97 
98  return NOTIFY_OK;
99 }
100 
101 static struct notifier_block __cpuinitdata blk_cpu_notifier = {
102  .notifier_call = blk_cpu_notify,
103 };
104 
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 = &__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)
149  } else if (raise_blk_irq(ccpu, req))
150  goto do_local;
151 
152  local_irq_restore(flags);
153 }
154 
167 {
168  if (unlikely(blk_should_fake_timeout(req->q)))
169  return;
170  if (!blk_mark_rq_complete(req))
172 }
174 
175 static __init int blk_softirq_init(void)
176 {
177  int i;
178 
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);