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 static LIST_HEAD(percpu_counters); 14 static DEFINE_MUTEX(percpu_counters_lock); 15 16 #ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER 17 18 static struct debug_obj_descr percpu_counter_debug_descr; 19 20 static int percpu_counter_fixup_free(void *addr, enum debug_obj_state state) 21 { 22 struct percpu_counter *fbc = addr; 23 24 switch (state) { 25 case ODEBUG_STATE_ACTIVE: 26 percpu_counter_destroy(fbc); 27 debug_object_free(fbc, &percpu_counter_debug_descr); 28 return 1; 29 default: 30 return 0; 31 } 32 } 33 34 static struct debug_obj_descr percpu_counter_debug_descr = { 35 .name = "percpu_counter", 36 .fixup_free = percpu_counter_fixup_free, 37 }; 38 39 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) 40 { 41 debug_object_init(fbc, &percpu_counter_debug_descr); 42 debug_object_activate(fbc, &percpu_counter_debug_descr); 43 } 44 45 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) 46 { 47 debug_object_deactivate(fbc, &percpu_counter_debug_descr); 48 debug_object_free(fbc, &percpu_counter_debug_descr); 49 } 50 51 #else /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ 52 static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) 53 { } 54 static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) 55 { } 56 #endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ 57 58 void percpu_counter_set(struct percpu_counter *fbc, s64 amount) 59 { 60 int cpu; 61 62 spin_lock(&fbc->lock); 63 for_each_possible_cpu(cpu) { 64 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 65 *pcount = 0; 66 } 67 fbc->count = amount; 68 spin_unlock(&fbc->lock); 69 } 70 EXPORT_SYMBOL(percpu_counter_set); 71 72 void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch) 73 { 74 s64 count; 75 76 preempt_disable(); 77 count = __this_cpu_read(*fbc->counters) + amount; 78 if (count >= batch || count <= -batch) { 79 spin_lock(&fbc->lock); 80 fbc->count += count; 81 __this_cpu_write(*fbc->counters, 0); 82 spin_unlock(&fbc->lock); 83 } else { 84 __this_cpu_write(*fbc->counters, count); 85 } 86 preempt_enable(); 87 } 88 EXPORT_SYMBOL(__percpu_counter_add); 89 90 /* 91 * Add up all the per-cpu counts, return the result. This is a more accurate 92 * but much slower version of percpu_counter_read_positive() 93 */ 94 s64 __percpu_counter_sum(struct percpu_counter *fbc) 95 { 96 s64 ret; 97 int cpu; 98 99 spin_lock(&fbc->lock); 100 ret = fbc->count; 101 for_each_online_cpu(cpu) { 102 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 103 ret += *pcount; 104 } 105 spin_unlock(&fbc->lock); 106 return ret; 107 } 108 EXPORT_SYMBOL(__percpu_counter_sum); 109 110 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, 111 struct lock_class_key *key) 112 { 113 spin_lock_init(&fbc->lock); 114 lockdep_set_class(&fbc->lock, key); 115 fbc->count = amount; 116 fbc->counters = alloc_percpu(s32); 117 if (!fbc->counters) 118 return -ENOMEM; 119 120 debug_percpu_counter_activate(fbc); 121 122 #ifdef CONFIG_HOTPLUG_CPU 123 INIT_LIST_HEAD(&fbc->list); 124 mutex_lock(&percpu_counters_lock); 125 list_add(&fbc->list, &percpu_counters); 126 mutex_unlock(&percpu_counters_lock); 127 #endif 128 return 0; 129 } 130 EXPORT_SYMBOL(__percpu_counter_init); 131 132 void percpu_counter_destroy(struct percpu_counter *fbc) 133 { 134 if (!fbc->counters) 135 return; 136 137 debug_percpu_counter_deactivate(fbc); 138 139 #ifdef CONFIG_HOTPLUG_CPU 140 mutex_lock(&percpu_counters_lock); 141 list_del(&fbc->list); 142 mutex_unlock(&percpu_counters_lock); 143 #endif 144 free_percpu(fbc->counters); 145 fbc->counters = NULL; 146 } 147 EXPORT_SYMBOL(percpu_counter_destroy); 148 149 int percpu_counter_batch __read_mostly = 32; 150 EXPORT_SYMBOL(percpu_counter_batch); 151 152 static void compute_batch_value(void) 153 { 154 int nr = num_online_cpus(); 155 156 percpu_counter_batch = max(32, nr*2); 157 } 158 159 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb, 160 unsigned long action, void *hcpu) 161 { 162 #ifdef CONFIG_HOTPLUG_CPU 163 unsigned int cpu; 164 struct percpu_counter *fbc; 165 166 compute_batch_value(); 167 if (action != CPU_DEAD) 168 return NOTIFY_OK; 169 170 cpu = (unsigned long)hcpu; 171 mutex_lock(&percpu_counters_lock); 172 list_for_each_entry(fbc, &percpu_counters, list) { 173 s32 *pcount; 174 unsigned long flags; 175 176 spin_lock_irqsave(&fbc->lock, flags); 177 pcount = per_cpu_ptr(fbc->counters, cpu); 178 fbc->count += *pcount; 179 *pcount = 0; 180 spin_unlock_irqrestore(&fbc->lock, flags); 181 } 182 mutex_unlock(&percpu_counters_lock); 183 #endif 184 return NOTIFY_OK; 185 } 186 187 /* 188 * Compare counter against given value. 189 * Return 1 if greater, 0 if equal and -1 if less 190 */ 191 int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs) 192 { 193 s64 count; 194 195 count = percpu_counter_read(fbc); 196 /* Check to see if rough count will be sufficient for comparison */ 197 if (abs(count - rhs) > (percpu_counter_batch*num_online_cpus())) { 198 if (count > rhs) 199 return 1; 200 else 201 return -1; 202 } 203 /* Need to use precise count */ 204 count = percpu_counter_sum(fbc); 205 if (count > rhs) 206 return 1; 207 else if (count < rhs) 208 return -1; 209 else 210 return 0; 211 } 212 EXPORT_SYMBOL(percpu_counter_compare); 213 214 static int __init percpu_counter_startup(void) 215 { 216 compute_batch_value(); 217 hotcpu_notifier(percpu_counter_hotcpu_callback, 0); 218 return 0; 219 } 220 module_init(percpu_counter_startup); 221