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(void) 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); 220