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         s32 *pcount;
  76
  77         preempt_disable();
  78         pcount = this_cpu_ptr(fbc->counters);
  79         count = *pcount + amount;
  80         if (count >= batch || count <= -batch) {
  81                 spin_lock(&fbc->lock);
  82                 fbc->count += count;
  83                 *pcount = 0;
  84                 spin_unlock(&fbc->lock);
  85         } else {
  86                 *pcount = 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         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         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         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         mutex_lock(&percpu_counters_lock);
 127         list_add(&fbc->list, &percpu_counters);
 128         mutex_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         mutex_lock(&percpu_counters_lock);
 143         list_del(&fbc->list);
 144         mutex_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         mutex_lock(&percpu_counters_lock);
 174         list_for_each_entry(fbc, &percpu_counters, list) {
 175                 s32 *pcount;
 176                 unsigned long flags;
 177
 178                 spin_lock_irqsave(&fbc->lock, flags);
 179                 pcount = per_cpu_ptr(fbc->counters, cpu);
 180                 fbc->count += *pcount;
 181                 *pcount = 0;
 182                 spin_unlock_irqrestore(&fbc->lock, flags);
 183         }
 184         mutex_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);