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 #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                 __this_cpu_sub(*fbc->counters, count - amount);
  86                 raw_spin_unlock_irqrestore(&fbc->lock, flags);
  87         } else {
  88                 this_cpu_add(*fbc->counters, amount);
  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);