1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Fast batching percpu counters. 4 */ 5 6 #include <linux/percpu_counter.h> 7 #include <linux/notifier.h> 8 #include <linux/mutex.h> 9 #include <linux/init.h> 10 #include <linux/cpu.h> 11 #include <linux/module.h> 12 #include <linux/debugobjects.h> 13 14 #ifdef CONFIG_HOTPLUG_CPU 15 static LIST_HEAD(percpu_counters); 16 static DEFINE_SPINLOCK(percpu_counters_lock); 17 #endif 18 19 #ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER 20 21 static struct debug_obj_descr percpu_counter_debug_descr; 22 23 static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state) 24 { 25 struct percpu_counter *fbc = addr; 26 27 switch (state) { 28 case ODEBUG_STATE_ACTIVE: 29 percpu_counter_destroy(fbc); 30 debug_object_free(fbc, &percpu_counter_debug_descr); 31 return true; 32 default: 33 return false; 34 } 35 } 36 37 static struct debug_obj_descr percpu_counter_debug_descr = { 38 .name = "percpu_counter", 39 .fixup_free = percpu_counter_fixup_free, 40 }; 41 42 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) 43 { 44 debug_object_init(fbc, &percpu_counter_debug_descr); 45 debug_object_activate(fbc, &percpu_counter_debug_descr); 46 } 47 48 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) 49 { 50 debug_object_deactivate(fbc, &percpu_counter_debug_descr); 51 debug_object_free(fbc, &percpu_counter_debug_descr); 52 } 53 54 #else /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ 55 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) 56 { } 57 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) 58 { } 59 #endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ 60 61 void percpu_counter_set(struct percpu_counter *fbc, s64 amount) 62 { 63 int cpu; 64 unsigned long flags; 65 66 raw_spin_lock_irqsave(&fbc->lock, flags); 67 for_each_possible_cpu(cpu) { 68 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 69 *pcount = 0; 70 } 71 fbc->count = amount; 72 raw_spin_unlock_irqrestore(&fbc->lock, flags); 73 } 74 EXPORT_SYMBOL(percpu_counter_set); 75 76 /** 77 * This function is both preempt and irq safe. The former is due to explicit 78 * preemption disable. The latter is guaranteed by the fact that the slow path 79 * is explicitly protected by an irq-safe spinlock whereas the fast patch uses 80 * this_cpu_add which is irq-safe by definition. Hence there is no need muck 81 * with irq state before calling this one 82 */ 83 void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch) 84 { 85 s64 count; 86 87 preempt_disable(); 88 count = __this_cpu_read(*fbc->counters) + amount; 89 if (count >= batch || count <= -batch) { 90 unsigned long flags; 91 raw_spin_lock_irqsave(&fbc->lock, flags); 92 fbc->count += count; 93 __this_cpu_sub(*fbc->counters, count - amount); 94 raw_spin_unlock_irqrestore(&fbc->lock, flags); 95 } else { 96 this_cpu_add(*fbc->counters, amount); 97 } 98 preempt_enable(); 99 } 100 EXPORT_SYMBOL(percpu_counter_add_batch); 101 102 /* 103 * Add up all the per-cpu counts, return the result. This is a more accurate 104 * but much slower version of percpu_counter_read_positive() 105 */ 106 s64 __percpu_counter_sum(struct percpu_counter *fbc) 107 { 108 s64 ret; 109 int cpu; 110 unsigned long flags; 111 112 raw_spin_lock_irqsave(&fbc->lock, flags); 113 ret = fbc->count; 114 for_each_online_cpu(cpu) { 115 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 116 ret += *pcount; 117 } 118 raw_spin_unlock_irqrestore(&fbc->lock, flags); 119 return ret; 120 } 121 EXPORT_SYMBOL(__percpu_counter_sum); 122 123 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp, 124 struct lock_class_key *key) 125 { 126 unsigned long flags __maybe_unused; 127 128 raw_spin_lock_init(&fbc->lock); 129 lockdep_set_class(&fbc->lock, key); 130 fbc->count = amount; 131 fbc->counters = alloc_percpu_gfp(s32, gfp); 132 if (!fbc->counters) 133 return -ENOMEM; 134 135 debug_percpu_counter_activate(fbc); 136 137 #ifdef CONFIG_HOTPLUG_CPU 138 INIT_LIST_HEAD(&fbc->list); 139 spin_lock_irqsave(&percpu_counters_lock, flags); 140 list_add(&fbc->list, &percpu_counters); 141 spin_unlock_irqrestore(&percpu_counters_lock, flags); 142 #endif 143 return 0; 144 } 145 EXPORT_SYMBOL(__percpu_counter_init); 146 147 void percpu_counter_destroy(struct percpu_counter *fbc) 148 { 149 unsigned long flags __maybe_unused; 150 151 if (!fbc->counters) 152 return; 153 154 debug_percpu_counter_deactivate(fbc); 155 156 #ifdef CONFIG_HOTPLUG_CPU 157 spin_lock_irqsave(&percpu_counters_lock, flags); 158 list_del(&fbc->list); 159 spin_unlock_irqrestore(&percpu_counters_lock, flags); 160 #endif 161 free_percpu(fbc->counters); 162 fbc->counters = NULL; 163 } 164 EXPORT_SYMBOL(percpu_counter_destroy); 165 166 int percpu_counter_batch __read_mostly = 32; 167 EXPORT_SYMBOL(percpu_counter_batch); 168 169 static int compute_batch_value(unsigned int cpu) 170 { 171 int nr = num_online_cpus(); 172 173 percpu_counter_batch = max(32, nr*2); 174 return 0; 175 } 176 177 static int percpu_counter_cpu_dead(unsigned int cpu) 178 { 179 #ifdef CONFIG_HOTPLUG_CPU 180 struct percpu_counter *fbc; 181 182 compute_batch_value(cpu); 183 184 spin_lock_irq(&percpu_counters_lock); 185 list_for_each_entry(fbc, &percpu_counters, list) { 186 s32 *pcount; 187 188 raw_spin_lock(&fbc->lock); 189 pcount = per_cpu_ptr(fbc->counters, cpu); 190 fbc->count += *pcount; 191 *pcount = 0; 192 raw_spin_unlock(&fbc->lock); 193 } 194 spin_unlock_irq(&percpu_counters_lock); 195 #endif 196 return 0; 197 } 198 199 /* 200 * Compare counter against given value. 201 * Return 1 if greater, 0 if equal and -1 if less 202 */ 203 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) 204 { 205 s64 count; 206 207 count = percpu_counter_read(fbc); 208 /* Check to see if rough count will be sufficient for comparison */ 209 if (abs(count - rhs) > (batch * num_online_cpus())) { 210 if (count > rhs) 211 return 1; 212 else 213 return -1; 214 } 215 /* Need to use precise count */ 216 count = percpu_counter_sum(fbc); 217 if (count > rhs) 218 return 1; 219 else if (count < rhs) 220 return -1; 221 else 222 return 0; 223 } 224 EXPORT_SYMBOL(__percpu_counter_compare); 225 226 static int __init percpu_counter_startup(void) 227 { 228 int ret; 229 230 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online", 231 compute_batch_value, NULL); 232 WARN_ON(ret < 0); 233 ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD, 234 "lib/percpu_cnt:dead", NULL, 235 percpu_counter_cpu_dead); 236 WARN_ON(ret < 0); 237 return 0; 238 } 239 module_init(percpu_counter_startup); 240