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 /* 126 * Add up all the per-cpu counts, return the result. This is a more accurate 127 * but much slower version of percpu_counter_read_positive(). 128 * 129 * We use the cpu mask of (cpu_online_mask | cpu_dying_mask) to capture sums 130 * from CPUs that are in the process of being taken offline. Dying cpus have 131 * been removed from the online mask, but may not have had the hotplug dead 132 * notifier called to fold the percpu count back into the global counter sum. 133 * By including dying CPUs in the iteration mask, we avoid this race condition 134 * so __percpu_counter_sum() just does the right thing when CPUs are being taken 135 * offline. 136 */ 137 s64 __percpu_counter_sum(struct percpu_counter *fbc) 138 { 139 s64 ret; 140 int cpu; 141 unsigned long flags; 142 143 raw_spin_lock_irqsave(&fbc->lock, flags); 144 ret = fbc->count; 145 for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) { 146 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 147 ret += *pcount; 148 } 149 raw_spin_unlock_irqrestore(&fbc->lock, flags); 150 return ret; 151 } 152 EXPORT_SYMBOL(__percpu_counter_sum); 153 154 int __percpu_counter_init_many(struct percpu_counter *fbc, s64 amount, 155 gfp_t gfp, u32 nr_counters, 156 struct lock_class_key *key) 157 { 158 unsigned long flags __maybe_unused; 159 size_t counter_size; 160 s32 __percpu *counters; 161 u32 i; 162 163 counter_size = ALIGN(sizeof(*counters), __alignof__(*counters)); 164 counters = __alloc_percpu_gfp(nr_counters * counter_size, 165 __alignof__(*counters), gfp); 166 if (!counters) { 167 fbc[0].counters = NULL; 168 return -ENOMEM; 169 } 170 171 for (i = 0; i < nr_counters; i++) { 172 raw_spin_lock_init(&fbc[i].lock); 173 lockdep_set_class(&fbc[i].lock, key); 174 #ifdef CONFIG_HOTPLUG_CPU 175 INIT_LIST_HEAD(&fbc[i].list); 176 #endif 177 fbc[i].count = amount; 178 fbc[i].counters = (void *)counters + (i * counter_size); 179 180 debug_percpu_counter_activate(&fbc[i]); 181 } 182 183 #ifdef CONFIG_HOTPLUG_CPU 184 spin_lock_irqsave(&percpu_counters_lock, flags); 185 for (i = 0; i < nr_counters; i++) 186 list_add(&fbc[i].list, &percpu_counters); 187 spin_unlock_irqrestore(&percpu_counters_lock, flags); 188 #endif 189 return 0; 190 } 191 EXPORT_SYMBOL(__percpu_counter_init_many); 192 193 void percpu_counter_destroy_many(struct percpu_counter *fbc, u32 nr_counters) 194 { 195 unsigned long flags __maybe_unused; 196 u32 i; 197 198 if (WARN_ON_ONCE(!fbc)) 199 return; 200 201 if (!fbc[0].counters) 202 return; 203 204 for (i = 0; i < nr_counters; i++) 205 debug_percpu_counter_deactivate(&fbc[i]); 206 207 #ifdef CONFIG_HOTPLUG_CPU 208 spin_lock_irqsave(&percpu_counters_lock, flags); 209 for (i = 0; i < nr_counters; i++) 210 list_del(&fbc[i].list); 211 spin_unlock_irqrestore(&percpu_counters_lock, flags); 212 #endif 213 214 free_percpu(fbc[0].counters); 215 216 for (i = 0; i < nr_counters; i++) 217 fbc[i].counters = NULL; 218 } 219 EXPORT_SYMBOL(percpu_counter_destroy_many); 220 221 int percpu_counter_batch __read_mostly = 32; 222 EXPORT_SYMBOL(percpu_counter_batch); 223 224 static int compute_batch_value(unsigned int cpu) 225 { 226 int nr = num_online_cpus(); 227 228 percpu_counter_batch = max(32, nr*2); 229 return 0; 230 } 231 232 static int percpu_counter_cpu_dead(unsigned int cpu) 233 { 234 #ifdef CONFIG_HOTPLUG_CPU 235 struct percpu_counter *fbc; 236 237 compute_batch_value(cpu); 238 239 spin_lock_irq(&percpu_counters_lock); 240 list_for_each_entry(fbc, &percpu_counters, list) { 241 s32 *pcount; 242 243 raw_spin_lock(&fbc->lock); 244 pcount = per_cpu_ptr(fbc->counters, cpu); 245 fbc->count += *pcount; 246 *pcount = 0; 247 raw_spin_unlock(&fbc->lock); 248 } 249 spin_unlock_irq(&percpu_counters_lock); 250 #endif 251 return 0; 252 } 253 254 /* 255 * Compare counter against given value. 256 * Return 1 if greater, 0 if equal and -1 if less 257 */ 258 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) 259 { 260 s64 count; 261 262 count = percpu_counter_read(fbc); 263 /* Check to see if rough count will be sufficient for comparison */ 264 if (abs(count - rhs) > (batch * num_online_cpus())) { 265 if (count > rhs) 266 return 1; 267 else 268 return -1; 269 } 270 /* Need to use precise count */ 271 count = percpu_counter_sum(fbc); 272 if (count > rhs) 273 return 1; 274 else if (count < rhs) 275 return -1; 276 else 277 return 0; 278 } 279 EXPORT_SYMBOL(__percpu_counter_compare); 280 281 static int __init percpu_counter_startup(void) 282 { 283 int ret; 284 285 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online", 286 compute_batch_value, NULL); 287 WARN_ON(ret < 0); 288 ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD, 289 "lib/percpu_cnt:dead", NULL, 290 percpu_counter_cpu_dead); 291 WARN_ON(ret < 0); 292 return 0; 293 } 294 module_init(percpu_counter_startup); 295