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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-11 08:27:49 +0000 |
commit | ace9429bb58fd418f0c81d4c2835699bddf6bde6 (patch) | |
tree | b2d64bc10158fdd5497876388cd68142ca374ed3 /lib/percpu_counter.c | |
parent | Initial commit. (diff) | |
download | linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.tar.xz linux-ace9429bb58fd418f0c81d4c2835699bddf6bde6.zip |
Adding upstream version 6.6.15.upstream/6.6.15
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | lib/percpu_counter.c | 294 |
1 files changed, 294 insertions, 0 deletions
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c new file mode 100644 index 0000000000..9073430dc8 --- /dev/null +++ b/lib/percpu_counter.c @@ -0,0 +1,294 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Fast batching percpu counters. + */ + +#include <linux/percpu_counter.h> +#include <linux/mutex.h> +#include <linux/init.h> +#include <linux/cpu.h> +#include <linux/module.h> +#include <linux/debugobjects.h> + +#ifdef CONFIG_HOTPLUG_CPU +static LIST_HEAD(percpu_counters); +static DEFINE_SPINLOCK(percpu_counters_lock); +#endif + +#ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER + +static const struct debug_obj_descr percpu_counter_debug_descr; + +static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state) +{ + struct percpu_counter *fbc = addr; + + switch (state) { + case ODEBUG_STATE_ACTIVE: + percpu_counter_destroy(fbc); + debug_object_free(fbc, &percpu_counter_debug_descr); + return true; + default: + return false; + } +} + +static const struct debug_obj_descr percpu_counter_debug_descr = { + .name = "percpu_counter", + .fixup_free = percpu_counter_fixup_free, +}; + +static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) +{ + debug_object_init(fbc, &percpu_counter_debug_descr); + debug_object_activate(fbc, &percpu_counter_debug_descr); +} + +static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) +{ + debug_object_deactivate(fbc, &percpu_counter_debug_descr); + debug_object_free(fbc, &percpu_counter_debug_descr); +} + +#else /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ +static inline void debug_percpu_counter_activate(struct percpu_counter *fbc) +{ } +static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc) +{ } +#endif /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */ + +void percpu_counter_set(struct percpu_counter *fbc, s64 amount) +{ + int cpu; + unsigned long flags; + + raw_spin_lock_irqsave(&fbc->lock, flags); + for_each_possible_cpu(cpu) { + s32 *pcount = per_cpu_ptr(fbc->counters, cpu); + *pcount = 0; + } + fbc->count = amount; + raw_spin_unlock_irqrestore(&fbc->lock, flags); +} +EXPORT_SYMBOL(percpu_counter_set); + +/* + * local_irq_save() is needed to make the function irq safe: + * - The slow path would be ok as protected by an irq-safe spinlock. + * - this_cpu_add would be ok as it is irq-safe by definition. + * But: + * The decision slow path/fast path and the actual update must be atomic, too. + * Otherwise a call in process context could check the current values and + * decide that the fast path can be used. If now an interrupt occurs before + * the this_cpu_add(), and the interrupt updates this_cpu(*fbc->counters), + * then the this_cpu_add() that is executed after the interrupt has completed + * can produce values larger than "batch" or even overflows. + */ +void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch) +{ + s64 count; + unsigned long flags; + + local_irq_save(flags); + count = __this_cpu_read(*fbc->counters) + amount; + if (abs(count) >= batch) { + raw_spin_lock(&fbc->lock); + fbc->count += count; + __this_cpu_sub(*fbc->counters, count - amount); + raw_spin_unlock(&fbc->lock); + } else { + this_cpu_add(*fbc->counters, amount); + } + local_irq_restore(flags); +} +EXPORT_SYMBOL(percpu_counter_add_batch); + +/* + * For percpu_counter with a big batch, the devication of its count could + * be big, and there is requirement to reduce the deviation, like when the + * counter's batch could be runtime decreased to get a better accuracy, + * which can be achieved by running this sync function on each CPU. + */ +void percpu_counter_sync(struct percpu_counter *fbc) +{ + unsigned long flags; + s64 count; + + raw_spin_lock_irqsave(&fbc->lock, flags); + count = __this_cpu_read(*fbc->counters); + fbc->count += count; + __this_cpu_sub(*fbc->counters, count); + raw_spin_unlock_irqrestore(&fbc->lock, flags); +} +EXPORT_SYMBOL(percpu_counter_sync); + +/* + * Add up all the per-cpu counts, return the result. This is a more accurate + * but much slower version of percpu_counter_read_positive(). + * + * We use the cpu mask of (cpu_online_mask | cpu_dying_mask) to capture sums + * from CPUs that are in the process of being taken offline. Dying cpus have + * been removed from the online mask, but may not have had the hotplug dead + * notifier called to fold the percpu count back into the global counter sum. + * By including dying CPUs in the iteration mask, we avoid this race condition + * so __percpu_counter_sum() just does the right thing when CPUs are being taken + * offline. + */ +s64 __percpu_counter_sum(struct percpu_counter *fbc) +{ + s64 ret; + int cpu; + unsigned long flags; + + raw_spin_lock_irqsave(&fbc->lock, flags); + ret = fbc->count; + for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) { + s32 *pcount = per_cpu_ptr(fbc->counters, cpu); + ret += *pcount; + } + raw_spin_unlock_irqrestore(&fbc->lock, flags); + return ret; +} +EXPORT_SYMBOL(__percpu_counter_sum); + +int __percpu_counter_init_many(struct percpu_counter *fbc, s64 amount, + gfp_t gfp, u32 nr_counters, + struct lock_class_key *key) +{ + unsigned long flags __maybe_unused; + size_t counter_size; + s32 __percpu *counters; + u32 i; + + counter_size = ALIGN(sizeof(*counters), __alignof__(*counters)); + counters = __alloc_percpu_gfp(nr_counters * counter_size, + __alignof__(*counters), gfp); + if (!counters) { + fbc[0].counters = NULL; + return -ENOMEM; + } + + for (i = 0; i < nr_counters; i++) { + raw_spin_lock_init(&fbc[i].lock); + lockdep_set_class(&fbc[i].lock, key); +#ifdef CONFIG_HOTPLUG_CPU + INIT_LIST_HEAD(&fbc[i].list); +#endif + fbc[i].count = amount; + fbc[i].counters = (void *)counters + (i * counter_size); + + debug_percpu_counter_activate(&fbc[i]); + } + +#ifdef CONFIG_HOTPLUG_CPU + spin_lock_irqsave(&percpu_counters_lock, flags); + for (i = 0; i < nr_counters; i++) + list_add(&fbc[i].list, &percpu_counters); + spin_unlock_irqrestore(&percpu_counters_lock, flags); +#endif + return 0; +} +EXPORT_SYMBOL(__percpu_counter_init_many); + +void percpu_counter_destroy_many(struct percpu_counter *fbc, u32 nr_counters) +{ + unsigned long flags __maybe_unused; + u32 i; + + if (WARN_ON_ONCE(!fbc)) + return; + + if (!fbc[0].counters) + return; + + for (i = 0; i < nr_counters; i++) + debug_percpu_counter_deactivate(&fbc[i]); + +#ifdef CONFIG_HOTPLUG_CPU + spin_lock_irqsave(&percpu_counters_lock, flags); + for (i = 0; i < nr_counters; i++) + list_del(&fbc[i].list); + spin_unlock_irqrestore(&percpu_counters_lock, flags); +#endif + + free_percpu(fbc[0].counters); + + for (i = 0; i < nr_counters; i++) + fbc[i].counters = NULL; +} +EXPORT_SYMBOL(percpu_counter_destroy_many); + +int percpu_counter_batch __read_mostly = 32; +EXPORT_SYMBOL(percpu_counter_batch); + +static int compute_batch_value(unsigned int cpu) +{ + int nr = num_online_cpus(); + + percpu_counter_batch = max(32, nr*2); + return 0; +} + +static int percpu_counter_cpu_dead(unsigned int cpu) +{ +#ifdef CONFIG_HOTPLUG_CPU + struct percpu_counter *fbc; + + compute_batch_value(cpu); + + spin_lock_irq(&percpu_counters_lock); + list_for_each_entry(fbc, &percpu_counters, list) { + s32 *pcount; + + raw_spin_lock(&fbc->lock); + pcount = per_cpu_ptr(fbc->counters, cpu); + fbc->count += *pcount; + *pcount = 0; + raw_spin_unlock(&fbc->lock); + } + spin_unlock_irq(&percpu_counters_lock); +#endif + return 0; +} + +/* + * Compare counter against given value. + * Return 1 if greater, 0 if equal and -1 if less + */ +int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch) +{ + s64 count; + + count = percpu_counter_read(fbc); + /* Check to see if rough count will be sufficient for comparison */ + if (abs(count - rhs) > (batch * num_online_cpus())) { + if (count > rhs) + return 1; + else + return -1; + } + /* Need to use precise count */ + count = percpu_counter_sum(fbc); + if (count > rhs) + return 1; + else if (count < rhs) + return -1; + else + return 0; +} +EXPORT_SYMBOL(__percpu_counter_compare); + +static int __init percpu_counter_startup(void) +{ + int ret; + + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online", + compute_batch_value, NULL); + WARN_ON(ret < 0); + ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD, + "lib/percpu_cnt:dead", NULL, + percpu_counter_cpu_dead); + WARN_ON(ret < 0); + return 0; +} +module_init(percpu_counter_startup); |