1 /* 2 * Fast batching percpu counters. 3 */ 4 5 #include <linux/percpu_counter.h> 6 #include <linux/notifier.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 void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch) 76 { 77 s64 count; 78 79 preempt_disable(); 80 count = __this_cpu_read(*fbc->counters) + amount; 81 if (count >= batch || count <= -batch) { 82 unsigned long flags; 83 raw_spin_lock_irqsave(&fbc->lock, flags); 84 fbc->count += count; 85 __this_cpu_sub(*fbc->counters, count - amount); 86 raw_spin_unlock_irqrestore(&fbc->lock, flags); 87 } else { 88 this_cpu_add(*fbc->counters, amount); 89 } 90 preempt_enable(); 91 } 92 EXPORT_SYMBOL(__percpu_counter_add); 93 94 /* 95 * Add up all the per-cpu counts, return the result. This is a more accurate 96 * but much slower version of percpu_counter_read_positive() 97 */ 98 s64 __percpu_counter_sum(struct percpu_counter *fbc) 99 { 100 s64 ret; 101 int cpu; 102 unsigned long flags; 103 104 raw_spin_lock_irqsave(&fbc->lock, flags); 105 ret = fbc->count; 106 for_each_online_cpu(cpu) { 107 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 108 ret += *pcount; 109 } 110 raw_spin_unlock_irqrestore(&fbc->lock, flags); 111 return ret; 112 } 113 EXPORT_SYMBOL(__percpu_counter_sum); 114 115 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp, 116 struct lock_class_key *key) 117 { 118 unsigned long flags __maybe_unused; 119 120 raw_spin_lock_init(&fbc->lock); 121 lockdep_set_class(&fbc->lock, key); 122 fbc->count = amount; 123 fbc->counters = alloc_percpu_gfp(s32, gfp); 124 if (!fbc->counters) 125 return -ENOMEM; 126 127 debug_percpu_counter_activate(fbc); 128 129 #ifdef CONFIG_HOTPLUG_CPU 130 INIT_LIST_HEAD(&fbc->list); 131 spin_lock_irqsave(&percpu_counters_lock, flags); 132 list_add(&fbc->list, &percpu_counters); 133 spin_unlock_irqrestore(&percpu_counters_lock, flags); 134 #endif 135 return 0; 136 } 137 EXPORT_SYMBOL(__percpu_counter_init); 138 139 void percpu_counter_destroy(struct percpu_counter *fbc) 140 { 141 unsigned long flags __maybe_unused; 142 143 if (!fbc->counters) 144 return; 145 146 debug_percpu_counter_deactivate(fbc); 147 148 #ifdef CONFIG_HOTPLUG_CPU 149 spin_lock_irqsave(&percpu_counters_lock, flags); 150 list_del(&fbc->list); 151 spin_unlock_irqrestore(&percpu_counters_lock, flags); 152 #endif 153 free_percpu(fbc->counters); 154 fbc->counters = NULL; 155 } 156 EXPORT_SYMBOL(percpu_counter_destroy); 157 158 int percpu_counter_batch __read_mostly = 32; 159 EXPORT_SYMBOL(percpu_counter_batch); 160 161 static int compute_batch_value(unsigned int cpu) 162 { 163 int nr = num_online_cpus(); 164 165 percpu_counter_batch = max(32, nr*2); 166 return 0; 167 } 168 169 static int percpu_counter_cpu_dead(unsigned int cpu) 170 { 171 #ifdef CONFIG_HOTPLUG_CPU 172 struct percpu_counter *fbc; 173 174 compute_batch_value(cpu); 175 176 spin_lock_irq(&percpu_counters_lock); 177 list_for_each_entry(fbc, &percpu_counters, list) { 178 s32 *pcount; 179 unsigned long flags; 180 181 raw_spin_lock_irqsave(&fbc->lock, flags); 182 pcount = per_cpu_ptr(fbc->counters, cpu); 183 fbc->count += *pcount; 184 *pcount = 0; 185 raw_spin_unlock_irqrestore(&fbc->lock, flags); 186 } 187 spin_unlock_irq(&percpu_counters_lock); 188 #endif 189 return 0; 190 } 191 192 /* 193 * Compare counter against given value. 194 * Return 1 if greater, 0 if equal and -1 if less 195 */ 196 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) 197 { 198 s64 count; 199 200 count = percpu_counter_read(fbc); 201 /* Check to see if rough count will be sufficient for comparison */ 202 if (abs(count - rhs) > (batch * num_online_cpus())) { 203 if (count > rhs) 204 return 1; 205 else 206 return -1; 207 } 208 /* Need to use precise count */ 209 count = percpu_counter_sum(fbc); 210 if (count > rhs) 211 return 1; 212 else if (count < rhs) 213 return -1; 214 else 215 return 0; 216 } 217 EXPORT_SYMBOL(__percpu_counter_compare); 218 219 static int __init percpu_counter_startup(void) 220 { 221 int ret; 222 223 ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online", 224 compute_batch_value, NULL); 225 WARN_ON(ret < 0); 226 ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD, 227 "lib/percpu_cnt:dead", NULL, 228 percpu_counter_cpu_dead); 229 WARN_ON(ret < 0); 230 return 0; 231 } 232 module_init(percpu_counter_startup); 233