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 * 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 (abs(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 * For percpu_counter with a big batch, the devication of its count could 103 * be big, and there is requirement to reduce the deviation, like when the 104 * counter's batch could be runtime decreased to get a better accuracy, 105 * which can be achieved by running this sync function on each CPU. 106 */ 107 void percpu_counter_sync(struct percpu_counter *fbc) 108 { 109 unsigned long flags; 110 s64 count; 111 112 raw_spin_lock_irqsave(&fbc->lock, flags); 113 count = __this_cpu_read(*fbc->counters); 114 fbc->count += count; 115 __this_cpu_sub(*fbc->counters, count); 116 raw_spin_unlock_irqrestore(&fbc->lock, flags); 117 } 118 EXPORT_SYMBOL(percpu_counter_sync); 119 120 /* 121 * Add up all the per-cpu counts, return the result. This is a more accurate 122 * but much slower version of percpu_counter_read_positive() 123 */ 124 s64 __percpu_counter_sum(struct percpu_counter *fbc) 125 { 126 s64 ret; 127 int cpu; 128 unsigned long flags; 129 130 raw_spin_lock_irqsave(&fbc->lock, flags); 131 ret = fbc->count; 132 for_each_online_cpu(cpu) { 133 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 134 ret += *pcount; 135 } 136 raw_spin_unlock_irqrestore(&fbc->lock, flags); 137 return ret; 138 } 139 EXPORT_SYMBOL(__percpu_counter_sum); 140 141 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp, 142 struct lock_class_key *key) 143 { 144 unsigned long flags __maybe_unused; 145 146 raw_spin_lock_init(&fbc->lock); 147 lockdep_set_class(&fbc->lock, key); 148 fbc->count = amount; 149 fbc->counters = alloc_percpu_gfp(s32, gfp); 150 if (!fbc->counters) 151 return -ENOMEM; 152 153 debug_percpu_counter_activate(fbc); 154 155 #ifdef CONFIG_HOTPLUG_CPU 156 INIT_LIST_HEAD(&fbc->list); 157 spin_lock_irqsave(&percpu_counters_lock, flags); 158 list_add(&fbc->list, &percpu_counters); 159 spin_unlock_irqrestore(&percpu_counters_lock, flags); 160 #endif 161 return 0; 162 } 163 EXPORT_SYMBOL(__percpu_counter_init); 164 165 void percpu_counter_destroy(struct percpu_counter *fbc) 166 { 167 unsigned long flags __maybe_unused; 168 169 if (!fbc->counters) 170 return; 171 172 debug_percpu_counter_deactivate(fbc); 173 174 #ifdef CONFIG_HOTPLUG_CPU 175 spin_lock_irqsave(&percpu_counters_lock, flags); 176 list_del(&fbc->list); 177 spin_unlock_irqrestore(&percpu_counters_lock, flags); 178 #endif 179 free_percpu(fbc->counters); 180 fbc->counters = NULL; 181 } 182 EXPORT_SYMBOL(percpu_counter_destroy); 183 184 int percpu_counter_batch __read_mostly = 32; 185 EXPORT_SYMBOL(percpu_counter_batch); 186 187 static int compute_batch_value(unsigned int cpu) 188 { 189 int nr = num_online_cpus(); 190 191 percpu_counter_batch = max(32, nr*2); 192 return 0; 193 } 194 195 static int percpu_counter_cpu_dead(unsigned int cpu) 196 { 197 #ifdef CONFIG_HOTPLUG_CPU 198 struct percpu_counter *fbc; 199 200 compute_batch_value(cpu); 201 202 spin_lock_irq(&percpu_counters_lock); 203 list_for_each_entry(fbc, &percpu_counters, list) { 204 s32 *pcount; 205 206 raw_spin_lock(&fbc->lock); 207 pcount = per_cpu_ptr(fbc->counters, cpu); 208 fbc->count += *pcount; 209 *pcount = 0; 210 raw_spin_unlock(&fbc->lock); 211 } 212 spin_unlock_irq(&percpu_counters_lock); 213 #endif 214 return 0; 215 } 216 217 /* 218 * Compare counter against given value. 219 * Return 1 if greater, 0 if equal and -1 if less 220 */ 221 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) 222 { 223 s64 count; 224 225 count = percpu_counter_read(fbc); 226 /* Check to see if rough count will be sufficient for comparison */ 227 if (abs(count - rhs) > (batch * num_online_cpus())) { 228 if (count > rhs) 229 return 1; 230 else 231 return -1; 232 } 233 /* Need to use precise count */ 234 count = percpu_counter_sum(fbc); 235 if (count > rhs) 236 return 1; 237 else if (count < rhs) 238 return -1; 239 else 240 return 0; 241 } 242 EXPORT_SYMBOL(__percpu_counter_compare); 243 244 static int __init percpu_counter_startup(void) 245 { 246 int ret; 247 248 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online", 249 compute_batch_value, NULL); 250 WARN_ON(ret < 0); 251 ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD, 252 "lib/percpu_cnt:dead", NULL, 253 percpu_counter_cpu_dead); 254 WARN_ON(ret < 0); 255 return 0; 256 } 257 module_init(percpu_counter_startup); 258