lib/percpu_counter.c

   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);