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         preempt_check_resched_rt();
  40 }
  41 EXPORT_SYMBOL(irq_poll_sched);
  42
  43 /**
  44  * __irq_poll_complete - Mark this @iop as un-polled again
  45  * @iop:      The parent iopoll structure
  46  *
  47  * Description:
  48  *     See irq_poll_complete(). This function must be called with interrupts
  49  *     disabled.
  50  **/
  51 static void __irq_poll_complete(struct irq_poll *iop)
  52 {
  53         list_del(&iop->list);
  54         smp_mb__before_atomic();
  55         clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
  56 }
  57
  58 /**
  59  * irq_poll_complete - Mark this @iop as un-polled again
  60  * @iop:      The parent iopoll structure
  61  *
  62  * Description:
  63  *     If a driver consumes less than the assigned budget in its run of the
  64  *     iopoll handler, it'll end the polled mode by calling this function. The
  65  *     iopoll handler will not be invoked again before irq_poll_sched()
  66  *     is called.
  67  **/
  68 void irq_poll_complete(struct irq_poll *iop)
  69 {
  70         unsigned long flags;
  71
  72         local_irq_save(flags);
  73         __irq_poll_complete(iop);
  74         local_irq_restore(flags);
  75         preempt_check_resched_rt();
  76 }
  77 EXPORT_SYMBOL(irq_poll_complete);
  78
  79 static void __latent_entropy irq_poll_softirq(struct softirq_action *h)
  80 {
  81         struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
  82         int rearm = 0, budget = irq_poll_budget;
  83         unsigned long start_time = jiffies;
  84
  85         local_irq_disable();
  86
  87         while (!list_empty(list)) {
  88                 struct irq_poll *iop;
  89                 int work, weight;
  90
  91                 /*
  92                  * If softirq window is exhausted then punt.
  93                  */
  94                 if (budget <= 0 || time_after(jiffies, start_time)) {
  95                         rearm = 1;
  96                         break;
  97                 }
  98
  99                 local_irq_enable();
 100                 preempt_check_resched_rt();
 101
 102                 /* Even though interrupts have been re-enabled, this
 103                  * access is safe because interrupts can only add new
 104                  * entries to the tail of this list, and only ->poll()
 105                  * calls can remove this head entry from the list.
 106                  */
 107                 iop = list_entry(list->next, struct irq_poll, list);
 108
 109                 weight = iop->weight;
 110                 work = 0;
 111                 if (test_bit(IRQ_POLL_F_SCHED, &iop->state))
 112                         work = iop->poll(iop, weight);
 113
 114                 budget -= work;
 115
 116                 local_irq_disable();
 117
 118                 /*
 119                  * Drivers must not modify the iopoll state, if they
 120                  * consume their assigned weight (or more, some drivers can't
 121                  * easily just stop processing, they have to complete an
 122                  * entire mask of commands).In such cases this code
 123                  * still "owns" the iopoll instance and therefore can
 124                  * move the instance around on the list at-will.
 125                  */
 126                 if (work >= weight) {
 127                         if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
 128                                 __irq_poll_complete(iop);
 129                         else
 130                                 list_move_tail(&iop->list, list);
 131                 }
 132         }
 133
 134         if (rearm)
 135                 __raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
 136
 137         local_irq_enable();
 138         preempt_check_resched_rt();
 139 }
 140
 141 /**
 142  * irq_poll_disable - Disable iopoll on this @iop
 143  * @iop:      The parent iopoll structure
 144  *
 145  * Description:
 146  *     Disable io polling and wait for any pending callbacks to have completed.
 147  **/
 148 void irq_poll_disable(struct irq_poll *iop)
 149 {
 150         set_bit(IRQ_POLL_F_DISABLE, &iop->state);
 151         while (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
 152                 msleep(1);
 153         clear_bit(IRQ_POLL_F_DISABLE, &iop->state);
 154 }
 155 EXPORT_SYMBOL(irq_poll_disable);
 156
 157 /**
 158  * irq_poll_enable - Enable iopoll on this @iop
 159  * @iop:      The parent iopoll structure
 160  *
 161  * Description:
 162  *     Enable iopoll on this @iop. Note that the handler run will not be
 163  *     scheduled, it will only mark it as active.
 164  **/
 165 void irq_poll_enable(struct irq_poll *iop)
 166 {
 167         BUG_ON(!test_bit(IRQ_POLL_F_SCHED, &iop->state));
 168         smp_mb__before_atomic();
 169         clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
 170 }
 171 EXPORT_SYMBOL(irq_poll_enable);
 172
 173 /**
 174  * irq_poll_init - Initialize this @iop
 175  * @iop:      The parent iopoll structure
 176  * @weight:   The default weight (or command completion budget)
 177  * @poll_fn:  The handler to invoke
 178  *
 179  * Description:
 180  *     Initialize and enable this irq_poll structure.
 181  **/
 182 void irq_poll_init(struct irq_poll *iop, int weight, irq_poll_fn *poll_fn)
 183 {
 184         memset(iop, 0, sizeof(*iop));
 185         INIT_LIST_HEAD(&iop->list);
 186         iop->weight = weight;
 187         iop->poll = poll_fn;
 188 }
 189 EXPORT_SYMBOL(irq_poll_init);
 190
 191 static int irq_poll_cpu_dead(unsigned int cpu)
 192 {
 193         /*
 194          * If a CPU goes away, splice its entries to the current CPU
 195          * and trigger a run of the softirq
 196          */
 197         local_irq_disable();
 198         list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
 199                          this_cpu_ptr(&blk_cpu_iopoll));
 200         __raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
 201         local_irq_enable();
 202         preempt_check_resched_rt();
 203
 204         return 0;
 205 }
 206
 207 static __init int irq_poll_setup(void)
 208 {
 209         int i;
 210
 211         for_each_possible_cpu(i)
 212                 INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
 213
 214         open_softirq(IRQ_POLL_SOFTIRQ, irq_poll_softirq);
 215         cpuhp_setup_state_nocalls(CPUHP_IRQ_POLL_DEAD, "irq_poll:dead", NULL,
 216                                   irq_poll_cpu_dead);
 217         return 0;
 218 }
 219 subsys_initcall(irq_poll_setup);