block/blk-iopoll.c

   1 /*
   2  * Functions related to interrupt-poll handling in the block layer. This
   3  * is similar to NAPI for network devices.
   4  */
   5 #include <linux/kernel.h>
   6 #include <linux/module.h>
   7 #include <linux/init.h>
   8 #include <linux/bio.h>
   9 #include <linux/blkdev.h>
  10 #include <linux/interrupt.h>
  11 #include <linux/cpu.h>
  12 #include <linux/blk-iopoll.h>
  13 #include <linux/delay.h>
  14
  15 #include "blk.h"
  16
  17 int blk_iopoll_enabled = 1;
  18 EXPORT_SYMBOL(blk_iopoll_enabled);
  19
  20 static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
  21
  22 /**
  23  * blk_iopoll_sched - Schedule a run of the iopoll handler
  24  * @iop:      The parent iopoll structure
  25  *
  26  * Description:
  27  *     Add this blk_iopoll structure to the pending poll list and trigger the raise
  28  *     of the blk iopoll softirq. The driver must already have gotten a succesful
  29  *     return from blk_iopoll_sched_prep() before calling this.
  30  **/
  31 void blk_iopoll_sched(struct blk_iopoll *iop)
  32 {
  33         unsigned long flags;
  34
  35         local_irq_save(flags);
  36         list_add_tail(&iop->list, &__get_cpu_var(blk_cpu_iopoll));
  37         __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
  38         local_irq_restore(flags);
  39 }
  40 EXPORT_SYMBOL(blk_iopoll_sched);
  41
  42 /**
  43  * __blk_iopoll_complete - Mark this @iop as un-polled again
  44  * @iop:      The parent iopoll structure
  45  *
  46  * Description:
  47  *     See blk_iopoll_complete(). This function must be called with interrupts disabled.
  48  **/
  49 void __blk_iopoll_complete(struct blk_iopoll *iop)
  50 {
  51         list_del(&iop->list);
  52         smp_mb__before_clear_bit();
  53         clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
  54 }
  55 EXPORT_SYMBOL(__blk_iopoll_complete);
  56
  57 /**
  58  * blk_iopoll_complete - Mark this @iop as un-polled again
  59  * @iop:      The parent iopoll structure
  60  *
  61  * Description:
  62  *     If a driver consumes less than the assigned budget in its run of the iopoll
  63  *     handler, it'll end the polled mode by calling this function. The iopoll handler
  64  *     will not be invoked again before blk_iopoll_sched_prep() is called.
  65  **/
  66 void blk_iopoll_complete(struct blk_iopoll *iopoll)
  67 {
  68         unsigned long flags;
  69
  70         local_irq_save(flags);
  71         __blk_iopoll_complete(iopoll);
  72         local_irq_restore(flags);
  73 }
  74 EXPORT_SYMBOL(blk_iopoll_complete);
  75
  76 static void blk_iopoll_softirq(struct softirq_action *h)
  77 {
  78         struct list_head *list = &__get_cpu_var(blk_cpu_iopoll);
  79         unsigned long start_time = jiffies;
  80         int rearm = 0, budget = 64;
  81
  82         local_irq_disable();
  83
  84         while (!list_empty(list)) {
  85                 struct blk_iopoll *iop;
  86                 int work, weight;
  87
  88                 /*
  89                  * If softirq window is exhausted then punt.
  90                  */
  91                 if (budget <= 0 || time_after(jiffies, start_time)) {
  92                         rearm = 1;
  93                         break;
  94                 }
  95
  96                 local_irq_enable();
  97
  98                 /* Even though interrupts have been re-enabled, this
  99                  * access is safe because interrupts can only add new
 100                  * entries to the tail of this list, and only ->poll()
 101                  * calls can remove this head entry from the list.
 102                  */
 103                 iop = list_entry(list->next, struct blk_iopoll, list);
 104
 105                 weight = iop->weight;
 106                 work = 0;
 107                 if (test_bit(IOPOLL_F_SCHED, &iop->state))
 108                         work = iop->poll(iop, weight);
 109
 110                 budget -= work;
 111
 112                 local_irq_disable();
 113
 114                 /* Drivers must not modify the NAPI state if they
 115                  * consume the entire weight.  In such cases this code
 116                  * still "owns" the NAPI instance and therefore can
 117                  * move the instance around on the list at-will.
 118                  */
 119                 if (work >= weight) {
 120                         if (blk_iopoll_disable_pending(iop))
 121                                 __blk_iopoll_complete(iop);
 122                         else
 123                                 list_move_tail(&iop->list, list);
 124                 }
 125         }
 126
 127         if (rearm)
 128                 __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
 129
 130         local_irq_enable();
 131 }
 132
 133 /**
 134  * blk_iopoll_disable - Disable iopoll on this @iop
 135  * @iop:      The parent iopoll structure
 136  *
 137  * Description:
 138  *     Disable io polling and wait for any pending callbacks to have completed.
 139  **/
 140 void blk_iopoll_disable(struct blk_iopoll *iop)
 141 {
 142         set_bit(IOPOLL_F_DISABLE, &iop->state);
 143         while (test_and_set_bit(IOPOLL_F_SCHED, &iop->state))
 144                 msleep(1);
 145         clear_bit(IOPOLL_F_DISABLE, &iop->state);
 146 }
 147 EXPORT_SYMBOL(blk_iopoll_disable);
 148
 149 /**
 150  * blk_iopoll_enable - Enable iopoll on this @iop
 151  * @iop:      The parent iopoll structure
 152  *
 153  * Description:
 154  *     Enable iopoll on this @iop. Note that the handler run will not be scheduled, it
 155  *     will only mark it as active.
 156  **/
 157 void blk_iopoll_enable(struct blk_iopoll *iop)
 158 {
 159         BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
 160         smp_mb__before_clear_bit();
 161         clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
 162 }
 163 EXPORT_SYMBOL(blk_iopoll_enable);
 164
 165 /**
 166  * blk_iopoll_init - Initialize this @iop
 167  * @iop:      The parent iopoll structure
 168  * @weight:   The default weight (or command completion budget)
 169  * @poll_fn:  The handler to invoke
 170  *
 171  * Description:
 172  *     Initialize this blk_iopoll structure. Before being actively used, the driver
 173  *     must call blk_iopoll_enable().
 174  **/
 175 void blk_iopoll_init(struct blk_iopoll *iop, int weight, blk_iopoll_fn *poll_fn)
 176 {
 177         memset(iop, 0, sizeof(*iop));
 178         INIT_LIST_HEAD(&iop->list);
 179         iop->weight = weight;
 180         iop->poll = poll_fn;
 181         set_bit(IOPOLL_F_SCHED, &iop->state);
 182 }
 183 EXPORT_SYMBOL(blk_iopoll_init);
 184
 185 static int __cpuinit blk_iopoll_cpu_notify(struct notifier_block *self,
 186                                           unsigned long action, void *hcpu)
 187 {
 188         /*
 189          * If a CPU goes away, splice its entries to the current CPU
 190          * and trigger a run of the softirq
 191          */
 192         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
 193                 int cpu = (unsigned long) hcpu;
 194
 195                 local_irq_disable();
 196                 list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
 197                                  &__get_cpu_var(blk_cpu_iopoll));
 198                 raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
 199                 local_irq_enable();
 200         }
 201
 202         return NOTIFY_OK;
 203 }
 204
 205 static struct notifier_block __cpuinitdata blk_iopoll_cpu_notifier = {
 206         .notifier_call  = blk_iopoll_cpu_notify,
 207 };
 208
 209 static __init int blk_iopoll_setup(void)
 210 {
 211         int i;
 212
 213         for_each_possible_cpu(i)
 214                 INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
 215
 216         open_softirq(BLOCK_IOPOLL_SOFTIRQ, blk_iopoll_softirq);
 217         register_hotcpu_notifier(&blk_iopoll_cpu_notifier);
 218         return 0;
 219 }
 220 subsys_initcall(blk_iopoll_setup);