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 const 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 const 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 * local_irq_save() is needed to make the function irq safe: 77 * - The slow path would be ok as protected by an irq-safe spinlock. 78 * - this_cpu_add would be ok as it is irq-safe by definition. 79 * But: 80 * The decision slow path/fast path and the actual update must be atomic, too. 81 * Otherwise a call in process context could check the current values and 82 * decide that the fast path can be used. If now an interrupt occurs before 83 * the this_cpu_add(), and the interrupt updates this_cpu(*fbc->counters), 84 * then the this_cpu_add() that is executed after the interrupt has completed 85 * can produce values larger than "batch" or even overflows. 86 */ 87 void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch) 88 { 89 s64 count; 90 unsigned long flags; 91 92 local_irq_save(flags); 93 count = __this_cpu_read(*fbc->counters) + amount; 94 if (abs(count) >= batch) { 95 raw_spin_lock(&fbc->lock); 96 fbc->count += count; 97 __this_cpu_sub(*fbc->counters, count - amount); 98 raw_spin_unlock(&fbc->lock); 99 } else { 100 this_cpu_add(*fbc->counters, amount); 101 } 102 local_irq_restore(flags); 103 } 104 EXPORT_SYMBOL(percpu_counter_add_batch); 105 106 /* 107 * For percpu_counter with a big batch, the devication of its count could 108 * be big, and there is requirement to reduce the deviation, like when the 109 * counter's batch could be runtime decreased to get a better accuracy, 110 * which can be achieved by running this sync function on each CPU. 111 */ 112 void percpu_counter_sync(struct percpu_counter *fbc) 113 { 114 unsigned long flags; 115 s64 count; 116 117 raw_spin_lock_irqsave(&fbc->lock, flags); 118 count = __this_cpu_read(*fbc->counters); 119 fbc->count += count; 120 __this_cpu_sub(*fbc->counters, count); 121 raw_spin_unlock_irqrestore(&fbc->lock, flags); 122 } 123 EXPORT_SYMBOL(percpu_counter_sync); 124 125 static s64 __percpu_counter_sum_mask(struct percpu_counter *fbc, 126 const struct cpumask *cpu_mask) 127 { 128 s64 ret; 129 int cpu; 130 unsigned long flags; 131 132 raw_spin_lock_irqsave(&fbc->lock, flags); 133 ret = fbc->count; 134 for_each_cpu(cpu, cpu_mask) { 135 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 136 ret += *pcount; 137 } 138 raw_spin_unlock_irqrestore(&fbc->lock, flags); 139 return ret; 140 } 141 142 /* 143 * Add up all the per-cpu counts, return the result. This is a more accurate 144 * but much slower version of percpu_counter_read_positive() 145 */ 146 s64 __percpu_counter_sum(struct percpu_counter *fbc) 147 { 148 return __percpu_counter_sum_mask(fbc, cpu_online_mask); 149 } 150 EXPORT_SYMBOL(__percpu_counter_sum); 151 152 /* 153 * This is slower version of percpu_counter_sum as it traverses all possible 154 * cpus. Use this only in the cases where accurate data is needed in the 155 * presense of CPUs getting offlined. 156 */ 157 s64 percpu_counter_sum_all(struct percpu_counter *fbc) 158 { 159 return __percpu_counter_sum_mask(fbc, cpu_possible_mask); 160 } 161 EXPORT_SYMBOL(percpu_counter_sum_all); 162 163 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp, 164 struct lock_class_key *key) 165 { 166 unsigned long flags __maybe_unused; 167 168 raw_spin_lock_init(&fbc->lock); 169 lockdep_set_class(&fbc->lock, key); 170 fbc->count = amount; 171 fbc->counters = alloc_percpu_gfp(s32, gfp); 172 if (!fbc->counters) 173 return -ENOMEM; 174 175 debug_percpu_counter_activate(fbc); 176 177 #ifdef CONFIG_HOTPLUG_CPU 178 INIT_LIST_HEAD(&fbc->list); 179 spin_lock_irqsave(&percpu_counters_lock, flags); 180 list_add(&fbc->list, &percpu_counters); 181 spin_unlock_irqrestore(&percpu_counters_lock, flags); 182 #endif 183 return 0; 184 } 185 EXPORT_SYMBOL(__percpu_counter_init); 186 187 void percpu_counter_destroy(struct percpu_counter *fbc) 188 { 189 unsigned long flags __maybe_unused; 190 191 if (!fbc->counters) 192 return; 193 194 debug_percpu_counter_deactivate(fbc); 195 196 #ifdef CONFIG_HOTPLUG_CPU 197 spin_lock_irqsave(&percpu_counters_lock, flags); 198 list_del(&fbc->list); 199 spin_unlock_irqrestore(&percpu_counters_lock, flags); 200 #endif 201 free_percpu(fbc->counters); 202 fbc->counters = NULL; 203 } 204 EXPORT_SYMBOL(percpu_counter_destroy); 205 206 int percpu_counter_batch __read_mostly = 32; 207 EXPORT_SYMBOL(percpu_counter_batch); 208 209 static int compute_batch_value(unsigned int cpu) 210 { 211 int nr = num_online_cpus(); 212 213 percpu_counter_batch = max(32, nr*2); 214 return 0; 215 } 216 217 static int percpu_counter_cpu_dead(unsigned int cpu) 218 { 219 #ifdef CONFIG_HOTPLUG_CPU 220 struct percpu_counter *fbc; 221 222 compute_batch_value(cpu); 223 224 spin_lock_irq(&percpu_counters_lock); 225 list_for_each_entry(fbc, &percpu_counters, list) { 226 s32 *pcount; 227 228 raw_spin_lock(&fbc->lock); 229 pcount = per_cpu_ptr(fbc->counters, cpu); 230 fbc->count += *pcount; 231 *pcount = 0; 232 raw_spin_unlock(&fbc->lock); 233 } 234 spin_unlock_irq(&percpu_counters_lock); 235 #endif 236 return 0; 237 } 238 239 /* 240 * Compare counter against given value. 241 * Return 1 if greater, 0 if equal and -1 if less 242 */ 243 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) 244 { 245 s64 count; 246 247 count = percpu_counter_read(fbc); 248 /* Check to see if rough count will be sufficient for comparison */ 249 if (abs(count - rhs) > (batch * num_online_cpus())) { 250 if (count > rhs) 251 return 1; 252 else 253 return -1; 254 } 255 /* Need to use precise count */ 256 count = percpu_counter_sum(fbc); 257 if (count > rhs) 258 return 1; 259 else if (count < rhs) 260 return -1; 261 else 262 return 0; 263 } 264 EXPORT_SYMBOL(__percpu_counter_compare); 265 266 static int __init percpu_counter_startup(void) 267 { 268 int ret; 269 270 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online", 271 compute_batch_value, NULL); 272 WARN_ON(ret < 0); 273 ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD, 274 "lib/percpu_cnt:dead", NULL, 275 percpu_counter_cpu_dead); 276 WARN_ON(ret < 0); 277 return 0; 278 } 279 module_init(percpu_counter_startup); 280