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Linux/lib/irq_poll.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/interrupt.h>
 10 #include <linux/cpu.h>
 11 #include <linux/irq_poll.h>
 12 #include <linux/delay.h>
 13 
 14 static unsigned int irq_poll_budget __read_mostly = 256;
 15 
 16 static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
 17 
 18 /**
 19  * irq_poll_sched - Schedule a run of the iopoll handler
 20  * @iop:      The parent iopoll structure
 21  *
 22  * Description:
 23  *     Add this irq_poll structure to the pending poll list and trigger the
 24  *     raise of the blk iopoll softirq.
 25  **/
 26 void irq_poll_sched(struct irq_poll *iop)
 27 {
 28         unsigned long flags;
 29 
 30         if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
 31                 return;
 32         if (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
 33                 return;
 34 
 35         local_irq_save(flags);
 36         list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
 37         __raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
 38         local_irq_restore(flags);
 39 }
 40 EXPORT_SYMBOL(irq_poll_sched);
 41 
 42 /**
 43  * __irq_poll_complete - Mark this @iop as un-polled again
 44  * @iop:      The parent iopoll structure
 45  *
 46  * Description:
 47  *     See irq_poll_complete(). This function must be called with interrupts
 48  *     disabled.
 49  **/
 50 static void __irq_poll_complete(struct irq_poll *iop)
 51 {
 52         list_del(&iop->list);
 53         smp_mb__before_atomic();
 54         clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
 55 }
 56 
 57 /**
 58  * irq_poll_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 irq_poll_sched()
 65  *     is called.
 66  **/
 67 void irq_poll_complete(struct irq_poll *iop)
 68 {
 69         unsigned long flags;
 70 
 71         local_irq_save(flags);
 72         __irq_poll_complete(iop);
 73         local_irq_restore(flags);
 74 }
 75 EXPORT_SYMBOL(irq_poll_complete);
 76 
 77 static void __latent_entropy irq_poll_softirq(struct softirq_action *h)
 78 {
 79         struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
 80         int rearm = 0, budget = irq_poll_budget;
 81         unsigned long start_time = jiffies;
 82 
 83         local_irq_disable();
 84 
 85         while (!list_empty(list)) {
 86                 struct irq_poll *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 irq_poll, list);
105 
106                 weight = iop->weight;
107                 work = 0;
108                 if (test_bit(IRQ_POLL_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 (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
125                                 __irq_poll_complete(iop);
126                         else
127                                 list_move_tail(&iop->list, list);
128                 }
129         }
130 
131         if (rearm)
132                 __raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
133 
134         local_irq_enable();
135 }
136 
137 /**
138  * irq_poll_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 irq_poll_disable(struct irq_poll *iop)
145 {
146         set_bit(IRQ_POLL_F_DISABLE, &iop->state);
147         while (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
148                 msleep(1);
149         clear_bit(IRQ_POLL_F_DISABLE, &iop->state);
150 }
151 EXPORT_SYMBOL(irq_poll_disable);
152 
153 /**
154  * irq_poll_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 irq_poll_enable(struct irq_poll *iop)
162 {
163         BUG_ON(!test_bit(IRQ_POLL_F_SCHED, &iop->state));
164         smp_mb__before_atomic();
165         clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
166 }
167 EXPORT_SYMBOL(irq_poll_enable);
168 
169 /**
170  * irq_poll_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 and enable this irq_poll structure.
177  **/
178 void irq_poll_init(struct irq_poll *iop, int weight, irq_poll_fn *poll_fn)
179 {
180         memset(iop, 0, sizeof(*iop));
181         INIT_LIST_HEAD(&iop->list);
182         iop->weight = weight;
183         iop->poll = poll_fn;
184 }
185 EXPORT_SYMBOL(irq_poll_init);
186 
187 static int irq_poll_cpu_dead(unsigned int cpu)
188 {
189         /*
190          * If a CPU goes away, splice its entries to the current CPU
191          * and trigger a run of the softirq
192          */
193         local_irq_disable();
194         list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
195                          this_cpu_ptr(&blk_cpu_iopoll));
196         __raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
197         local_irq_enable();
198 
199         return 0;
200 }
201 
202 static __init int irq_poll_setup(void)
203 {
204         int i;
205 
206         for_each_possible_cpu(i)
207                 INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
208 
209         open_softirq(IRQ_POLL_SOFTIRQ, irq_poll_softirq);
210         cpuhp_setup_state_nocalls(CPUHP_IRQ_POLL_DEAD, "irq_poll:dead", NULL,
211                                   irq_poll_cpu_dead);
212         return 0;
213 }
214 subsys_initcall(irq_poll_setup);
215 

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