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 int 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 1; 31 default: 32 return 0; 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 64 raw_spin_lock(&fbc->lock); 65 for_each_possible_cpu(cpu) { 66 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 67 *pcount = 0; 68 } 69 fbc->count = amount; 70 raw_spin_unlock(&fbc->lock); 71 } 72 EXPORT_SYMBOL(percpu_counter_set); 73 74 void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch) 75 { 76 s64 count; 77 78 preempt_disable(); 79 count = __this_cpu_read(*fbc->counters) + amount; 80 if (count >= batch || count <= -batch) { 81 raw_spin_lock(&fbc->lock); 82 fbc->count += count; 83 __this_cpu_write(*fbc->counters, 0); 84 raw_spin_unlock(&fbc->lock); 85 } else { 86 __this_cpu_write(*fbc->counters, count); 87 } 88 preempt_enable(); 89 } 90 EXPORT_SYMBOL(__percpu_counter_add); 91 92 /* 93 * Add up all the per-cpu counts, return the result. This is a more accurate 94 * but much slower version of percpu_counter_read_positive() 95 */ 96 s64 __percpu_counter_sum(struct percpu_counter *fbc) 97 { 98 s64 ret; 99 int cpu; 100 101 raw_spin_lock(&fbc->lock); 102 ret = fbc->count; 103 for_each_online_cpu(cpu) { 104 s32 *pcount = per_cpu_ptr(fbc->counters, cpu); 105 ret += *pcount; 106 } 107 raw_spin_unlock(&fbc->lock); 108 return ret; 109 } 110 EXPORT_SYMBOL(__percpu_counter_sum); 111 112 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, 113 struct lock_class_key *key) 114 { 115 raw_spin_lock_init(&fbc->lock); 116 lockdep_set_class(&fbc->lock, key); 117 fbc->count = amount; 118 fbc->counters = alloc_percpu(s32); 119 if (!fbc->counters) 120 return -ENOMEM; 121 122 debug_percpu_counter_activate(fbc); 123 124 #ifdef CONFIG_HOTPLUG_CPU 125 INIT_LIST_HEAD(&fbc->list); 126 spin_lock(&percpu_counters_lock); 127 list_add(&fbc->list, &percpu_counters); 128 spin_unlock(&percpu_counters_lock); 129 #endif 130 return 0; 131 } 132 EXPORT_SYMBOL(__percpu_counter_init); 133 134 void percpu_counter_destroy(struct percpu_counter *fbc) 135 { 136 if (!fbc->counters) 137 return; 138 139 debug_percpu_counter_deactivate(fbc); 140 141 #ifdef CONFIG_HOTPLUG_CPU 142 spin_lock(&percpu_counters_lock); 143 list_del(&fbc->list); 144 spin_unlock(&percpu_counters_lock); 145 #endif 146 free_percpu(fbc->counters); 147 fbc->counters = NULL; 148 } 149 EXPORT_SYMBOL(percpu_counter_destroy); 150 151 int percpu_counter_batch __read_mostly = 32; 152 EXPORT_SYMBOL(percpu_counter_batch); 153 154 static void compute_batch_value(void) 155 { 156 int nr = num_online_cpus(); 157 158 percpu_counter_batch = max(32, nr*2); 159 } 160 161 static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb, 162 unsigned long action, void *hcpu) 163 { 164 #ifdef CONFIG_HOTPLUG_CPU 165 unsigned int cpu; 166 struct percpu_counter *fbc; 167 168 compute_batch_value(); 169 if (action != CPU_DEAD) 170 return NOTIFY_OK; 171 172 cpu = (unsigned long)hcpu; 173 spin_lock(&percpu_counters_lock); 174 list_for_each_entry(fbc, &percpu_counters, list) { 175 s32 *pcount; 176 unsigned long flags; 177 178 raw_spin_lock_irqsave(&fbc->lock, flags); 179 pcount = per_cpu_ptr(fbc->counters, cpu); 180 fbc->count += *pcount; 181 *pcount = 0; 182 raw_spin_unlock_irqrestore(&fbc->lock, flags); 183 } 184 spin_unlock(&percpu_counters_lock); 185 #endif 186 return NOTIFY_OK; 187 } 188 189 /* 190 * Compare counter against given value. 191 * Return 1 if greater, 0 if equal and -1 if less 192 */ 193 int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs) 194 { 195 s64 count; 196 197 count = percpu_counter_read(fbc); 198 /* Check to see if rough count will be sufficient for comparison */ 199 if (abs(count - rhs) > (percpu_counter_batch*num_online_cpus())) { 200 if (count > rhs) 201 return 1; 202 else 203 return -1; 204 } 205 /* Need to use precise count */ 206 count = percpu_counter_sum(fbc); 207 if (count > rhs) 208 return 1; 209 else if (count < rhs) 210 return -1; 211 else 212 return 0; 213 } 214 EXPORT_SYMBOL(percpu_counter_compare); 215 216 static int __init percpu_counter_startup(void) 217 { 218 compute_batch_value(); 219 hotcpu_notifier(percpu_counter_hotcpu_callback, 0); 220 return 0; 221 } 222 module_init(percpu_counter_startup); 223