271 lines
7.2 KiB
C
271 lines
7.2 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Fast batching percpu counters.
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*/
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#include <linux/percpu_counter.h>
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#include <linux/mutex.h>
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#include <linux/init.h>
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#include <linux/cpu.h>
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#include <linux/module.h>
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#include <linux/debugobjects.h>
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#ifdef CONFIG_HOTPLUG_CPU
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static LIST_HEAD(percpu_counters);
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static DEFINE_SPINLOCK(percpu_counters_lock);
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#endif
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#ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER
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static const struct debug_obj_descr percpu_counter_debug_descr;
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static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state)
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{
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struct percpu_counter *fbc = addr;
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switch (state) {
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case ODEBUG_STATE_ACTIVE:
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percpu_counter_destroy(fbc);
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debug_object_free(fbc, &percpu_counter_debug_descr);
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return true;
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default:
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return false;
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}
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}
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static const struct debug_obj_descr percpu_counter_debug_descr = {
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.name = "percpu_counter",
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.fixup_free = percpu_counter_fixup_free,
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};
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static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
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{
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debug_object_init(fbc, &percpu_counter_debug_descr);
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debug_object_activate(fbc, &percpu_counter_debug_descr);
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}
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static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
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{
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debug_object_deactivate(fbc, &percpu_counter_debug_descr);
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debug_object_free(fbc, &percpu_counter_debug_descr);
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}
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#else /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
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static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
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{ }
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static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
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{ }
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#endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
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void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
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{
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int cpu;
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unsigned long flags;
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raw_spin_lock_irqsave(&fbc->lock, flags);
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for_each_possible_cpu(cpu) {
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s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
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*pcount = 0;
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}
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fbc->count = amount;
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raw_spin_unlock_irqrestore(&fbc->lock, flags);
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}
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EXPORT_SYMBOL(percpu_counter_set);
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/*
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* local_irq_save() is needed to make the function irq safe:
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* - The slow path would be ok as protected by an irq-safe spinlock.
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* - this_cpu_add would be ok as it is irq-safe by definition.
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* But:
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* The decision slow path/fast path and the actual update must be atomic, too.
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* Otherwise a call in process context could check the current values and
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* decide that the fast path can be used. If now an interrupt occurs before
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* the this_cpu_add(), and the interrupt updates this_cpu(*fbc->counters),
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* then the this_cpu_add() that is executed after the interrupt has completed
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* can produce values larger than "batch" or even overflows.
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*/
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void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
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{
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s64 count;
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unsigned long flags;
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local_irq_save(flags);
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count = __this_cpu_read(*fbc->counters) + amount;
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if (abs(count) >= batch) {
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raw_spin_lock(&fbc->lock);
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fbc->count += count;
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__this_cpu_sub(*fbc->counters, count - amount);
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raw_spin_unlock(&fbc->lock);
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} else {
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this_cpu_add(*fbc->counters, amount);
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}
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local_irq_restore(flags);
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}
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EXPORT_SYMBOL(percpu_counter_add_batch);
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/*
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* For percpu_counter with a big batch, the devication of its count could
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* be big, and there is requirement to reduce the deviation, like when the
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* counter's batch could be runtime decreased to get a better accuracy,
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* which can be achieved by running this sync function on each CPU.
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*/
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void percpu_counter_sync(struct percpu_counter *fbc)
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{
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unsigned long flags;
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s64 count;
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raw_spin_lock_irqsave(&fbc->lock, flags);
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count = __this_cpu_read(*fbc->counters);
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fbc->count += count;
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__this_cpu_sub(*fbc->counters, count);
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raw_spin_unlock_irqrestore(&fbc->lock, flags);
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}
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EXPORT_SYMBOL(percpu_counter_sync);
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/*
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* Add up all the per-cpu counts, return the result. This is a more accurate
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* but much slower version of percpu_counter_read_positive().
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*
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* We use the cpu mask of (cpu_online_mask | cpu_dying_mask) to capture sums
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* from CPUs that are in the process of being taken offline. Dying cpus have
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* been removed from the online mask, but may not have had the hotplug dead
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* notifier called to fold the percpu count back into the global counter sum.
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* By including dying CPUs in the iteration mask, we avoid this race condition
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* so __percpu_counter_sum() just does the right thing when CPUs are being taken
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* offline.
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*/
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s64 __percpu_counter_sum(struct percpu_counter *fbc)
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{
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s64 ret;
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int cpu;
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unsigned long flags;
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raw_spin_lock_irqsave(&fbc->lock, flags);
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ret = fbc->count;
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for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) {
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s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
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ret += *pcount;
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}
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raw_spin_unlock_irqrestore(&fbc->lock, flags);
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return ret;
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}
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EXPORT_SYMBOL(__percpu_counter_sum);
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int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
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struct lock_class_key *key)
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{
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unsigned long flags __maybe_unused;
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raw_spin_lock_init(&fbc->lock);
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lockdep_set_class(&fbc->lock, key);
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fbc->count = amount;
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fbc->counters = alloc_percpu_gfp(s32, gfp);
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if (!fbc->counters)
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return -ENOMEM;
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debug_percpu_counter_activate(fbc);
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#ifdef CONFIG_HOTPLUG_CPU
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INIT_LIST_HEAD(&fbc->list);
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spin_lock_irqsave(&percpu_counters_lock, flags);
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list_add(&fbc->list, &percpu_counters);
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spin_unlock_irqrestore(&percpu_counters_lock, flags);
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#endif
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return 0;
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}
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EXPORT_SYMBOL(__percpu_counter_init);
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void percpu_counter_destroy(struct percpu_counter *fbc)
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{
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unsigned long flags __maybe_unused;
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if (!fbc->counters)
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return;
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debug_percpu_counter_deactivate(fbc);
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#ifdef CONFIG_HOTPLUG_CPU
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spin_lock_irqsave(&percpu_counters_lock, flags);
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list_del(&fbc->list);
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spin_unlock_irqrestore(&percpu_counters_lock, flags);
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#endif
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free_percpu(fbc->counters);
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fbc->counters = NULL;
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}
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EXPORT_SYMBOL(percpu_counter_destroy);
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int percpu_counter_batch __read_mostly = 32;
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EXPORT_SYMBOL(percpu_counter_batch);
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static int compute_batch_value(unsigned int cpu)
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{
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int nr = num_online_cpus();
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percpu_counter_batch = max(32, nr*2);
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return 0;
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}
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static int percpu_counter_cpu_dead(unsigned int cpu)
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{
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#ifdef CONFIG_HOTPLUG_CPU
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struct percpu_counter *fbc;
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compute_batch_value(cpu);
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spin_lock_irq(&percpu_counters_lock);
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list_for_each_entry(fbc, &percpu_counters, list) {
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s32 *pcount;
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raw_spin_lock(&fbc->lock);
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pcount = per_cpu_ptr(fbc->counters, cpu);
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fbc->count += *pcount;
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*pcount = 0;
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raw_spin_unlock(&fbc->lock);
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}
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spin_unlock_irq(&percpu_counters_lock);
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#endif
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return 0;
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}
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/*
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* Compare counter against given value.
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* Return 1 if greater, 0 if equal and -1 if less
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*/
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int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
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{
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s64 count;
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count = percpu_counter_read(fbc);
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/* Check to see if rough count will be sufficient for comparison */
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if (abs(count - rhs) > (batch * num_online_cpus())) {
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if (count > rhs)
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return 1;
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else
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return -1;
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}
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/* Need to use precise count */
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count = percpu_counter_sum(fbc);
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if (count > rhs)
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return 1;
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else if (count < rhs)
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return -1;
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else
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return 0;
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}
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EXPORT_SYMBOL(__percpu_counter_compare);
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static int __init percpu_counter_startup(void)
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{
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int ret;
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ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online",
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compute_batch_value, NULL);
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WARN_ON(ret < 0);
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ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD,
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"lib/percpu_cnt:dead", NULL,
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percpu_counter_cpu_dead);
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WARN_ON(ret < 0);
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return 0;
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}
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module_init(percpu_counter_startup);
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