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 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_notify(struct notifier_block *self, 188 unsigned long action, void *hcpu) 189 { 190 /* 191 * If a CPU goes away, splice its entries to the current CPU 192 * and trigger a run of the softirq 193 */ 194 if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) { 195 int cpu = (unsigned long) hcpu; 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 } 203 204 return NOTIFY_OK; 205 } 206 207 static struct notifier_block irq_poll_cpu_notifier = { 208 .notifier_call = irq_poll_cpu_notify, 209 }; 210 211 static __init int irq_poll_setup(void) 212 { 213 int i; 214 215 for_each_possible_cpu(i) 216 INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i)); 217 218 open_softirq(IRQ_POLL_SOFTIRQ, irq_poll_softirq); 219 register_hotcpu_notifier(&irq_poll_cpu_notifier); 220 return 0; 221 } 222 subsys_initcall(irq_poll_setup); 223