1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Fast batching percpu counters. 4 */ 5 6 #include <linux/percpu_counter.h> 7 #include <linux/mutex.h> 8 #include <linux/init.h> 9 #include <linux/cpu.h> 10 #include <linux/module.h> 11 #include <linux/debugobjects.h> 12 13 #ifdef CONFIG_HOTPLUG_CPU 14 static LIST_HEAD(percpu_counters); 15 static DEFINE_SPINLOCK(percpu_counters_lock); 16 #endif 17 18 #ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER 19 20 static struct debug_obj_descr percpu_counter_debug_descr; 21 22 static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state) 23 { 24 struct percpu_counter *fbc = addr; 25 26 switch (state) { 27 case ODEBUG_STATE_ACTIVE: 28 percpu_counter_destroy(fbc); 29 debug_object_free(fbc, &percpu_counter_debug_descr); 30 return true; 31 default: 32 return false; 33 } 34 } 35 36 static struct debug_obj_descr percpu_counter_debug_descr = { 37 .name = "percpu_counter", 38 .fixup_free = percpu_counter_fixup_free, 39 }; 40 41 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) 42 { 43 debug_object_init(fbc, &percpu_counter_debug_descr); 44 debug_object_activate(fbc, &percpu_counter_debug_descr); 45 } 46 47 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) 48 { 49 debug_object_deactivate(fbc, &percpu_counter_debug_descr); 50 debug_object_free(fbc, &percpu_counter_debug_descr); 51 } 52 53 #else /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ 54 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) 55 { } 56 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) 57 { } 58 #endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ 59 60 void percpu_counter_set(struct percpu_counter *fbc, s64 amount) 61 { 62 int cpu; 63 unsigned long flags; 64 65 raw_spin_lock_irqsave(&fbc->lock, flags); 66 for_each_possible_cpu(cpu) { 67 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 68 *pcount = 0; 69 } 70 fbc->count = amount; 71 raw_spin_unlock_irqrestore(&fbc->lock, flags); 72 } 73 EXPORT_SYMBOL(percpu_counter_set); 74 75 /** 76 * This function is both preempt and irq safe. The former is due to explicit 77 * preemption disable. The latter is guaranteed by the fact that the slow path 78 * is explicitly protected by an irq-safe spinlock whereas the fast patch uses 79 * this_cpu_add which is irq-safe by definition. Hence there is no need muck 80 * with irq state before calling this one 81 */ 82 void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch) 83 { 84 s64 count; 85 86 preempt_disable(); 87 count = __this_cpu_read(*fbc->counters) + amount; 88 if (count >= batch || count <= -batch) { 89 unsigned long flags; 90 raw_spin_lock_irqsave(&fbc->lock, flags); 91 fbc->count += count; 92 __this_cpu_sub(*fbc->counters, count - amount); 93 raw_spin_unlock_irqrestore(&fbc->lock, flags); 94 } else { 95 this_cpu_add(*fbc->counters, amount); 96 } 97 preempt_enable(); 98 } 99 EXPORT_SYMBOL(percpu_counter_add_batch); 100 101 /* 102 * Add up all the per-cpu counts, return the result. This is a more accurate 103 * but much slower version of percpu_counter_read_positive() 104 */ 105 s64 __percpu_counter_sum(struct percpu_counter *fbc) 106 { 107 s64 ret; 108 int cpu; 109 unsigned long flags; 110 111 raw_spin_lock_irqsave(&fbc->lock, flags); 112 ret = fbc->count; 113 for_each_online_cpu(cpu) { 114 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 115 ret += *pcount; 116 } 117 raw_spin_unlock_irqrestore(&fbc->lock, flags); 118 return ret; 119 } 120 EXPORT_SYMBOL(__percpu_counter_sum); 121 122 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp, 123 struct lock_class_key *key) 124 { 125 unsigned long flags __maybe_unused; 126 127 raw_spin_lock_init(&fbc->lock); 128 lockdep_set_class(&fbc->lock, key); 129 fbc->count = amount; 130 fbc->counters = alloc_percpu_gfp(s32, gfp); 131 if (!fbc->counters) 132 return -ENOMEM; 133 134 debug_percpu_counter_activate(fbc); 135 136 #ifdef CONFIG_HOTPLUG_CPU 137 INIT_LIST_HEAD(&fbc->list); 138 spin_lock_irqsave(&percpu_counters_lock, flags); 139 list_add(&fbc->list, &percpu_counters); 140 spin_unlock_irqrestore(&percpu_counters_lock, flags); 141 #endif 142 return 0; 143 } 144 EXPORT_SYMBOL(__percpu_counter_init); 145 146 void percpu_counter_destroy(struct percpu_counter *fbc) 147 { 148 unsigned long flags __maybe_unused; 149 150 if (!fbc->counters) 151 return; 152 153 debug_percpu_counter_deactivate(fbc); 154 155 #ifdef CONFIG_HOTPLUG_CPU 156 spin_lock_irqsave(&percpu_counters_lock, flags); 157 list_del(&fbc->list); 158 spin_unlock_irqrestore(&percpu_counters_lock, flags); 159 #endif 160 free_percpu(fbc->counters); 161 fbc->counters = NULL; 162 } 163 EXPORT_SYMBOL(percpu_counter_destroy); 164 165 int percpu_counter_batch __read_mostly = 32; 166 EXPORT_SYMBOL(percpu_counter_batch); 167 168 static int compute_batch_value(unsigned int cpu) 169 { 170 int nr = num_online_cpus(); 171 172 percpu_counter_batch = max(32, nr*2); 173 return 0; 174 } 175 176 static int percpu_counter_cpu_dead(unsigned int cpu) 177 { 178 #ifdef CONFIG_HOTPLUG_CPU 179 struct percpu_counter *fbc; 180 181 compute_batch_value(cpu); 182 183 spin_lock_irq(&percpu_counters_lock); 184 list_for_each_entry(fbc, &percpu_counters, list) { 185 s32 *pcount; 186 187 raw_spin_lock(&fbc->lock); 188 pcount = per_cpu_ptr(fbc->counters, cpu); 189 fbc->count += *pcount; 190 *pcount = 0; 191 raw_spin_unlock(&fbc->lock); 192 } 193 spin_unlock_irq(&percpu_counters_lock); 194 #endif 195 return 0; 196 } 197 198 /* 199 * Compare counter against given value. 200 * Return 1 if greater, 0 if equal and -1 if less 201 */ 202 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) 203 { 204 s64 count; 205 206 count = percpu_counter_read(fbc); 207 /* Check to see if rough count will be sufficient for comparison */ 208 if (abs(count - rhs) > (batch * num_online_cpus())) { 209 if (count > rhs) 210 return 1; 211 else 212 return -1; 213 } 214 /* Need to use precise count */ 215 count = percpu_counter_sum(fbc); 216 if (count > rhs) 217 return 1; 218 else if (count < rhs) 219 return -1; 220 else 221 return 0; 222 } 223 EXPORT_SYMBOL(__percpu_counter_compare); 224 225 static int __init percpu_counter_startup(void) 226 { 227 int ret; 228 229 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online", 230 compute_batch_value, NULL); 231 WARN_ON(ret < 0); 232 ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD, 233 "lib/percpu_cnt:dead", NULL, 234 percpu_counter_cpu_dead); 235 WARN_ON(ret < 0); 236 return 0; 237 } 238 module_init(percpu_counter_startup); 239