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);