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 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 raw_spin_unlock_irqrestore(&fbc->lock, flags); 86 __this_cpu_write(*fbc->counters, 0); 87 } else { 88 __this_cpu_write(*fbc->counters, count); 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, 116 struct lock_class_key *key) 117 { 118 raw_spin_lock_init(&fbc->lock); 119 lockdep_set_class(&fbc->lock, key); 120 fbc->count = amount; 121 fbc->counters = alloc_percpu(s32); 122 if (!fbc->counters) 123 return -ENOMEM; 124 125 debug_percpu_counter_activate(fbc); 126 127 #ifdef CONFIG_HOTPLUG_CPU 128 INIT_LIST_HEAD(&fbc->list); 129 spin_lock(&percpu_counters_lock); 130 list_add(&fbc->list, &percpu_counters); 131 spin_unlock(&percpu_counters_lock); 132 #endif 133 return 0; 134 } 135 EXPORT_SYMBOL(__percpu_counter_init); 136 137 void percpu_counter_destroy(struct percpu_counter *fbc) 138 { 139 if (!fbc->counters) 140 return; 141 142 debug_percpu_counter_deactivate(fbc); 143 144 #ifdef CONFIG_HOTPLUG_CPU 145 spin_lock(&percpu_counters_lock); 146 list_del(&fbc->list); 147 spin_unlock(&percpu_counters_lock); 148 #endif 149 free_percpu(fbc->counters); 150 fbc->counters = NULL; 151 } 152 EXPORT_SYMBOL(percpu_counter_destroy); 153 154 int percpu_counter_batch __read_mostly = 32; 155 EXPORT_SYMBOL(percpu_counter_batch); 156 157 static void compute_batch_value(void) 158 { 159 int nr = num_online_cpus(); 160 161 percpu_counter_batch = max(32, nr*2); 162 } 163 164 static int percpu_counter_hotcpu_callback(struct notifier_block *nb, 165 unsigned long action, void *hcpu) 166 { 167 #ifdef CONFIG_HOTPLUG_CPU 168 unsigned int cpu; 169 struct percpu_counter *fbc; 170 171 compute_batch_value(); 172 if (action != CPU_DEAD) 173 return NOTIFY_OK; 174 175 cpu = (unsigned long)hcpu; 176 spin_lock(&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(&percpu_counters_lock); 188 #endif 189 return NOTIFY_OK; 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) 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) > (percpu_counter_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 compute_batch_value(); 222 hotcpu_notifier(percpu_counter_hotcpu_callback, 0); 223 return 0; 224 } 225 module_init(percpu_counter_startup); 226