lib/percpu_counter.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Fast batching percpu counters.
   4  */
   5
   6 #include <linux/percpu_counter.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 const struct debug_obj_descr percpu_counter_debug_descr;
  21
  22 static bool 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 true;
  31         default:
  32                 return false;
  33         }
  34 }
  35
  36 static const 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 /**
  76  * This function is both preempt and irq safe. The former is due to explicit
  77  * preemption disable. The latter is guaranteed by the fact that the slow path
  78  * is explicitly protected by an irq-safe spinlock whereas the fast patch uses
  79  * this_cpu_add which is irq-safe by definition. Hence there is no need muck
  80  * with irq state before calling this one
  81  */
  82 void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
  83 {
  84         s64 count;
  85
  86         preempt_disable();
  87         count = __this_cpu_read(*fbc->counters) + amount;
  88         if (abs(count) >= batch) {
  89                 unsigned long flags;
  90                 raw_spin_lock_irqsave(&fbc->lock, flags);
  91                 fbc->count += count;
  92                 __this_cpu_sub(*fbc->counters, count - amount);
  93                 raw_spin_unlock_irqrestore(&fbc->lock, flags);
  94         } else {
  95                 this_cpu_add(*fbc->counters, amount);
  96         }
  97         preempt_enable();
  98 }
  99 EXPORT_SYMBOL(percpu_counter_add_batch);
 100
 101 /*
 102  * For percpu_counter with a big batch, the devication of its count could
 103  * be big, and there is requirement to reduce the deviation, like when the
 104  * counter's batch could be runtime decreased to get a better accuracy,
 105  * which can be achieved by running this sync function on each CPU.
 106  */
 107 void percpu_counter_sync(struct percpu_counter *fbc)
 108 {
 109         unsigned long flags;
 110         s64 count;
 111
 112         raw_spin_lock_irqsave(&fbc->lock, flags);
 113         count = __this_cpu_read(*fbc->counters);
 114         fbc->count += count;
 115         __this_cpu_sub(*fbc->counters, count);
 116         raw_spin_unlock_irqrestore(&fbc->lock, flags);
 117 }
 118 EXPORT_SYMBOL(percpu_counter_sync);
 119
 120 /*
 121  * Add up all the per-cpu counts, return the result.  This is a more accurate
 122  * but much slower version of percpu_counter_read_positive()
 123  */
 124 s64 __percpu_counter_sum(struct percpu_counter *fbc)
 125 {
 126         s64 ret;
 127         int cpu;
 128         unsigned long flags;
 129
 130         raw_spin_lock_irqsave(&fbc->lock, flags);
 131         ret = fbc->count;
 132         for_each_online_cpu(cpu) {
 133                 s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
 134                 ret += *pcount;
 135         }
 136         raw_spin_unlock_irqrestore(&fbc->lock, flags);
 137         return ret;
 138 }
 139 EXPORT_SYMBOL(__percpu_counter_sum);
 140
 141 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
 142                           struct lock_class_key *key)
 143 {
 144         unsigned long flags __maybe_unused;
 145
 146         raw_spin_lock_init(&fbc->lock);
 147         lockdep_set_class(&fbc->lock, key);
 148         fbc->count = amount;
 149         fbc->counters = alloc_percpu_gfp(s32, gfp);
 150         if (!fbc->counters)
 151                 return -ENOMEM;
 152
 153         debug_percpu_counter_activate(fbc);
 154
 155 #ifdef CONFIG_HOTPLUG_CPU
 156         INIT_LIST_HEAD(&fbc->list);
 157         spin_lock_irqsave(&percpu_counters_lock, flags);
 158         list_add(&fbc->list, &percpu_counters);
 159         spin_unlock_irqrestore(&percpu_counters_lock, flags);
 160 #endif
 161         return 0;
 162 }
 163 EXPORT_SYMBOL(__percpu_counter_init);
 164
 165 void percpu_counter_destroy(struct percpu_counter *fbc)
 166 {
 167         unsigned long flags __maybe_unused;
 168
 169         if (!fbc->counters)
 170                 return;
 171
 172         debug_percpu_counter_deactivate(fbc);
 173
 174 #ifdef CONFIG_HOTPLUG_CPU
 175         spin_lock_irqsave(&percpu_counters_lock, flags);
 176         list_del(&fbc->list);
 177         spin_unlock_irqrestore(&percpu_counters_lock, flags);
 178 #endif
 179         free_percpu(fbc->counters);
 180         fbc->counters = NULL;
 181 }
 182 EXPORT_SYMBOL(percpu_counter_destroy);
 183
 184 int percpu_counter_batch __read_mostly = 32;
 185 EXPORT_SYMBOL(percpu_counter_batch);
 186
 187 static int compute_batch_value(unsigned int cpu)
 188 {
 189         int nr = num_online_cpus();
 190
 191         percpu_counter_batch = max(32, nr*2);
 192         return 0;
 193 }
 194
 195 static int percpu_counter_cpu_dead(unsigned int cpu)
 196 {
 197 #ifdef CONFIG_HOTPLUG_CPU
 198         struct percpu_counter *fbc;
 199
 200         compute_batch_value(cpu);
 201
 202         spin_lock_irq(&percpu_counters_lock);
 203         list_for_each_entry(fbc, &percpu_counters, list) {
 204                 s32 *pcount;
 205
 206                 raw_spin_lock(&fbc->lock);
 207                 pcount = per_cpu_ptr(fbc->counters, cpu);
 208                 fbc->count += *pcount;
 209                 *pcount = 0;
 210                 raw_spin_unlock(&fbc->lock);
 211         }
 212         spin_unlock_irq(&percpu_counters_lock);
 213 #endif
 214         return 0;
 215 }
 216
 217 /*
 218  * Compare counter against given value.
 219  * Return 1 if greater, 0 if equal and -1 if less
 220  */
 221 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
 222 {
 223         s64     count;
 224
 225         count = percpu_counter_read(fbc);
 226         /* Check to see if rough count will be sufficient for comparison */
 227         if (abs(count - rhs) > (batch * num_online_cpus())) {
 228                 if (count > rhs)
 229                         return 1;
 230                 else
 231                         return -1;
 232         }
 233         /* Need to use precise count */
 234         count = percpu_counter_sum(fbc);
 235         if (count > rhs)
 236                 return 1;
 237         else if (count < rhs)
 238                 return -1;
 239         else
 240                 return 0;
 241 }
 242 EXPORT_SYMBOL(__percpu_counter_compare);
 243
 244 static int __init percpu_counter_startup(void)
 245 {
 246         int ret;
 247
 248         ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online",
 249                                 compute_batch_value, NULL);
 250         WARN_ON(ret < 0);
 251         ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD,
 252                                         "lib/percpu_cnt:dead", NULL,
 253                                         percpu_counter_cpu_dead);
 254         WARN_ON(ret < 0);
 255         return 0;
 256 }
 257 module_init(percpu_counter_startup);