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TOMOYO Linux Cross Reference
Linux/block/blk-iopoll.c

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  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 static unsigned int blk_iopoll_budget __read_mostly = 256;
 18 
 19 static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
 20 
 21 /**
 22  * blk_iopoll_sched - Schedule a run of the iopoll handler
 23  * @iop:      The parent iopoll structure
 24  *
 25  * Description:
 26  *     Add this blk_iopoll structure to the pending poll list and trigger the
 27  *     raise of the blk iopoll softirq. The driver must already have gotten a
 28  *     successful return from blk_iopoll_sched_prep() before calling this.
 29  **/
 30 void blk_iopoll_sched(struct blk_iopoll *iop)
 31 {
 32         unsigned long flags;
 33 
 34         local_irq_save(flags);
 35         list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
 36         __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
 37         local_irq_restore(flags);
 38 }
 39 EXPORT_SYMBOL(blk_iopoll_sched);
 40 
 41 /**
 42  * __blk_iopoll_complete - Mark this @iop as un-polled again
 43  * @iop:      The parent iopoll structure
 44  *
 45  * Description:
 46  *     See blk_iopoll_complete(). This function must be called with interrupts
 47  *     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
 63  *     iopoll handler, it'll end the polled mode by calling this function. The
 64  *     iopoll handler will not be invoked again before blk_iopoll_sched_prep()
 65  *     is called.
 66  **/
 67 void blk_iopoll_complete(struct blk_iopoll *iopoll)
 68 {
 69         unsigned long flags;
 70 
 71         local_irq_save(flags);
 72         __blk_iopoll_complete(iopoll);
 73         local_irq_restore(flags);
 74 }
 75 EXPORT_SYMBOL(blk_iopoll_complete);
 76 
 77 static void blk_iopoll_softirq(struct softirq_action *h)
 78 {
 79         struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
 80         int rearm = 0, budget = blk_iopoll_budget;
 81         unsigned long start_time = jiffies;
 82 
 83         local_irq_disable();
 84 
 85         while (!list_empty(list)) {
 86                 struct blk_iopoll *iop;
 87                 int work, weight;
 88 
 89                 /*
 90                  * If softirq window is exhausted then punt.
 91                  */
 92                 if (budget <= 0 || time_after(jiffies, start_time)) {
 93                         rearm = 1;
 94                         break;
 95                 }
 96 
 97                 local_irq_enable();
 98 
 99                 /* Even though interrupts have been re-enabled, this
100                  * access is safe because interrupts can only add new
101                  * entries to the tail of this list, and only ->poll()
102                  * calls can remove this head entry from the list.
103                  */
104                 iop = list_entry(list->next, struct blk_iopoll, list);
105 
106                 weight = iop->weight;
107                 work = 0;
108                 if (test_bit(IOPOLL_F_SCHED, &iop->state))
109                         work = iop->poll(iop, weight);
110 
111                 budget -= work;
112 
113                 local_irq_disable();
114 
115                 /*
116                  * Drivers must not modify the iopoll state, if they
117                  * consume their assigned weight (or more, some drivers can't
118                  * easily just stop processing, they have to complete an
119                  * entire mask of commands).In such cases this code
120                  * still "owns" the iopoll instance and therefore can
121                  * move the instance around on the list at-will.
122                  */
123                 if (work >= weight) {
124                         if (blk_iopoll_disable_pending(iop))
125                                 __blk_iopoll_complete(iop);
126                         else
127                                 list_move_tail(&iop->list, list);
128                 }
129         }
130 
131         if (rearm)
132                 __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
133 
134         local_irq_enable();
135 }
136 
137 /**
138  * blk_iopoll_disable - Disable iopoll on this @iop
139  * @iop:      The parent iopoll structure
140  *
141  * Description:
142  *     Disable io polling and wait for any pending callbacks to have completed.
143  **/
144 void blk_iopoll_disable(struct blk_iopoll *iop)
145 {
146         set_bit(IOPOLL_F_DISABLE, &iop->state);
147         while (test_and_set_bit(IOPOLL_F_SCHED, &iop->state))
148                 msleep(1);
149         clear_bit(IOPOLL_F_DISABLE, &iop->state);
150 }
151 EXPORT_SYMBOL(blk_iopoll_disable);
152 
153 /**
154  * blk_iopoll_enable - Enable iopoll on this @iop
155  * @iop:      The parent iopoll structure
156  *
157  * Description:
158  *     Enable iopoll on this @iop. Note that the handler run will not be
159  *     scheduled, it will only mark it as active.
160  **/
161 void blk_iopoll_enable(struct blk_iopoll *iop)
162 {
163         BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
164         smp_mb__before_clear_bit();
165         clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
166 }
167 EXPORT_SYMBOL(blk_iopoll_enable);
168 
169 /**
170  * blk_iopoll_init - Initialize this @iop
171  * @iop:      The parent iopoll structure
172  * @weight:   The default weight (or command completion budget)
173  * @poll_fn:  The handler to invoke
174  *
175  * Description:
176  *     Initialize this blk_iopoll structure. Before being actively used, the
177  *     driver must call blk_iopoll_enable().
178  **/
179 void blk_iopoll_init(struct blk_iopoll *iop, int weight, blk_iopoll_fn *poll_fn)
180 {
181         memset(iop, 0, sizeof(*iop));
182         INIT_LIST_HEAD(&iop->list);
183         iop->weight = weight;
184         iop->poll = poll_fn;
185         set_bit(IOPOLL_F_SCHED, &iop->state);
186 }
187 EXPORT_SYMBOL(blk_iopoll_init);
188 
189 static int blk_iopoll_cpu_notify(struct notifier_block *self,
190                                  unsigned long action, void *hcpu)
191 {
192         /*
193          * If a CPU goes away, splice its entries to the current CPU
194          * and trigger a run of the softirq
195          */
196         if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
197                 int cpu = (unsigned long) hcpu;
198 
199                 local_irq_disable();
200                 list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
201                                  this_cpu_ptr(&blk_cpu_iopoll));
202                 __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
203                 local_irq_enable();
204         }
205 
206         return NOTIFY_OK;
207 }
208 
209 static struct notifier_block blk_iopoll_cpu_notifier = {
210         .notifier_call  = blk_iopoll_cpu_notify,
211 };
212 
213 static __init int blk_iopoll_setup(void)
214 {
215         int i;
216 
217         for_each_possible_cpu(i)
218                 INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
219 
220         open_softirq(BLOCK_IOPOLL_SOFTIRQ, blk_iopoll_softirq);
221         register_hotcpu_notifier(&blk_iopoll_cpu_notifier);
222         return 0;
223 }
224 subsys_initcall(blk_iopoll_setup);
225 

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