diff options
Diffstat (limited to 'lib/percpu_counter.c')
| -rw-r--r-- | lib/percpu_counter.c | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c new file mode 100644 index 00000000..209448e1 --- /dev/null +++ b/lib/percpu_counter.c @@ -0,0 +1,174 @@ +/* + * Fast batching percpu counters. + */ + +#include <linux/percpu_counter.h> +#include <linux/notifier.h> +#include <linux/mutex.h> +#include <linux/init.h> +#include <linux/cpu.h> +#include <linux/module.h> + +static LIST_HEAD(percpu_counters); +static DEFINE_MUTEX(percpu_counters_lock); + +void percpu_counter_set(struct percpu_counter *fbc, s64 amount) +{ + int cpu; + + spin_lock(&fbc->lock); + for_each_possible_cpu(cpu) { + s32 *pcount = per_cpu_ptr(fbc->counters, cpu); + *pcount = 0; + } + fbc->count = amount; + spin_unlock(&fbc->lock); +} +EXPORT_SYMBOL(percpu_counter_set); + +void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch) +{ + s64 count; + s32 *pcount; + int cpu = get_cpu(); + + pcount = per_cpu_ptr(fbc->counters, cpu); + count = *pcount + amount; + if (count >= batch || count <= -batch) { + spin_lock(&fbc->lock); + fbc->count += count; + *pcount = 0; + spin_unlock(&fbc->lock); + } else { + *pcount = count; + } + put_cpu(); +} +EXPORT_SYMBOL(__percpu_counter_add); + +/* + * Add up all the per-cpu counts, return the result. This is a more accurate + * but much slower version of percpu_counter_read_positive() + */ +s64 __percpu_counter_sum(struct percpu_counter *fbc) +{ + s64 ret; + int cpu; + + spin_lock(&fbc->lock); + ret = fbc->count; + for_each_online_cpu(cpu) { + s32 *pcount = per_cpu_ptr(fbc->counters, cpu); + ret += *pcount; + } + spin_unlock(&fbc->lock); + return ret; +} +EXPORT_SYMBOL(__percpu_counter_sum); + +int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, + struct lock_class_key *key) +{ + spin_lock_init(&fbc->lock); + lockdep_set_class(&fbc->lock, key); + fbc->count = amount; + fbc->counters = alloc_percpu(s32); + if (!fbc->counters) + return -ENOMEM; +#ifdef CONFIG_HOTPLUG_CPU + INIT_LIST_HEAD(&fbc->list); + mutex_lock(&percpu_counters_lock); + list_add(&fbc->list, &percpu_counters); + mutex_unlock(&percpu_counters_lock); +#endif + return 0; +} +EXPORT_SYMBOL(__percpu_counter_init); + +void percpu_counter_destroy(struct percpu_counter *fbc) +{ + if (!fbc->counters) + return; + +#ifdef CONFIG_HOTPLUG_CPU + mutex_lock(&percpu_counters_lock); + list_del(&fbc->list); + mutex_unlock(&percpu_counters_lock); +#endif + free_percpu(fbc->counters); + fbc->counters = NULL; +} +EXPORT_SYMBOL(percpu_counter_destroy); + +int percpu_counter_batch __read_mostly = 32; +EXPORT_SYMBOL(percpu_counter_batch); + +static void compute_batch_value(void) +{ + int nr = num_online_cpus(); + + percpu_counter_batch = max(32, nr*2); +} + +static int __cpuinit percpu_counter_hotcpu_callback(struct notifier_block *nb, + unsigned long action, void *hcpu) +{ +#ifdef CONFIG_HOTPLUG_CPU + unsigned int cpu; + struct percpu_counter *fbc; + + compute_batch_value(); + if (action != CPU_DEAD) + return NOTIFY_OK; + + cpu = (unsigned long)hcpu; + mutex_lock(&percpu_counters_lock); + list_for_each_entry(fbc, &percpu_counters, list) { + s32 *pcount; + unsigned long flags; + + spin_lock_irqsave(&fbc->lock, flags); + pcount = per_cpu_ptr(fbc->counters, cpu); + fbc->count += *pcount; + *pcount = 0; + spin_unlock_irqrestore(&fbc->lock, flags); + } + mutex_unlock(&percpu_counters_lock); +#endif + return NOTIFY_OK; +} + +/* + * 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) +{ + s64 count; + + count = percpu_counter_read(fbc); + /* Check to see if rough count will be sufficient for comparison */ + if (abs(count - rhs) > (percpu_counter_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) +{ + compute_batch_value(); + hotcpu_notifier(percpu_counter_hotcpu_callback, 0); + return 0; +} +module_init(percpu_counter_startup); |