lib/irq_poll.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Functions related to interrupt-poll handling in the block layer. This
   4  * is similar to NAPI for network devices.
   5  */
   6 #include <linux/kernel.h>
   7 #include <linux/module.h>
   8 #include <linux/init.h>
   9 #include <linux/bio.h>
  10 #include <linux/interrupt.h>
  11 #include <linux/cpu.h>
  12 #include <linux/irq_poll.h>
  13 #include <linux/delay.h>
  14
  15 static unsigned int irq_poll_budget __read_mostly = 256;
  16
  17 static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
  18
  19 /**
  20  * irq_poll_sched - Schedule a run of the iopoll handler
  21  * @iop:      The parent iopoll structure
  22  *
  23  * Description:
  24  *     Add this irq_poll structure to the pending poll list and trigger the
  25  *     raise of the blk iopoll softirq.
  26  **/
  27 void irq_poll_sched(struct irq_poll *iop)
  28 {
  29         unsigned long flags;
  30
  31         if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
  32                 return;
  33         if (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
  34                 return;
  35
  36         local_irq_save(flags);
  37         list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
  38         raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
  39         local_irq_restore(flags);
  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 }
  76 EXPORT_SYMBOL(irq_poll_complete);
  77
  78 static void __latent_entropy irq_poll_softirq(struct softirq_action *h)
  79 {
  80         struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
  81         int rearm = 0, budget = irq_poll_budget;
  82         unsigned long start_time = jiffies;
  83
  84         local_irq_disable();
  85
  86         while (!list_empty(list)) {
  87                 struct irq_poll *iop;
  88                 int work, weight;
  89
  90                 /*
  91                  * If softirq window is exhausted then punt.
  92                  */
  93                 if (budget <= 0 || time_after(jiffies, start_time)) {
  94                         rearm = 1;
  95                         break;
  96                 }
  97
  98                 local_irq_enable();
  99
 100                 /* Even though interrupts have been re-enabled, this
 101                  * access is safe because interrupts can only add new
 102                  * entries to the tail of this list, and only ->poll()
 103                  * calls can remove this head entry from the list.
 104                  */
 105                 iop = list_entry(list->next, struct irq_poll, list);
 106
 107                 weight = iop->weight;
 108                 work = 0;
 109                 if (test_bit(IRQ_POLL_F_SCHED, &iop->state))
 110                         work = iop->poll(iop, weight);
 111
 112                 budget -= work;
 113
 114                 local_irq_disable();
 115
 116                 /*
 117                  * Drivers must not modify the iopoll state, if they
 118                  * consume their assigned weight (or more, some drivers can't
 119                  * easily just stop processing, they have to complete an
 120                  * entire mask of commands).In such cases this code
 121                  * still "owns" the iopoll instance and therefore can
 122                  * move the instance around on the list at-will.
 123                  */
 124                 if (work >= weight) {
 125                         if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
 126                                 __irq_poll_complete(iop);
 127                         else
 128                                 list_move_tail(&iop->list, list);
 129                 }
 130         }
 131
 132         if (rearm)
 133                 __raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
 134
 135         local_irq_enable();
 136 }
 137
 138 /**
 139  * irq_poll_disable - Disable iopoll on this @iop
 140  * @iop:      The parent iopoll structure
 141  *
 142  * Description:
 143  *     Disable io polling and wait for any pending callbacks to have completed.
 144  **/
 145 void irq_poll_disable(struct irq_poll *iop)
 146 {
 147         set_bit(IRQ_POLL_F_DISABLE, &iop->state);
 148         while (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
 149                 msleep(1);
 150         clear_bit(IRQ_POLL_F_DISABLE, &iop->state);
 151 }
 152 EXPORT_SYMBOL(irq_poll_disable);
 153
 154 /**
 155  * irq_poll_enable - Enable iopoll on this @iop
 156  * @iop:      The parent iopoll structure
 157  *
 158  * Description:
 159  *     Enable iopoll on this @iop. Note that the handler run will not be
 160  *     scheduled, it will only mark it as active.
 161  **/
 162 void irq_poll_enable(struct irq_poll *iop)
 163 {
 164         BUG_ON(!test_bit(IRQ_POLL_F_SCHED, &iop->state));
 165         smp_mb__before_atomic();
 166         clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
 167 }
 168 EXPORT_SYMBOL(irq_poll_enable);
 169
 170 /**
 171  * irq_poll_init - Initialize this @iop
 172  * @iop:      The parent iopoll structure
 173  * @weight:   The default weight (or command completion budget)
 174  * @poll_fn:  The handler to invoke
 175  *
 176  * Description:
 177  *     Initialize and enable this irq_poll structure.
 178  **/
 179 void irq_poll_init(struct irq_poll *iop, int weight, irq_poll_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 }
 186 EXPORT_SYMBOL(irq_poll_init);
 187
 188 static int irq_poll_cpu_dead(unsigned int cpu)
 189 {
 190         /*
 191          * If a CPU goes away, splice its entries to the current CPU and
 192          * set the POLL softirq bit. The local_bh_disable()/enable() pair
 193          * ensures that it is handled. Otherwise the current CPU could
 194          * reach idle with the POLL softirq pending.
 195          */
 196         local_bh_disable();
 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         local_bh_enable();
 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);