From: Waiman Long Subject: [PATCH v2 1/4] percpu_stats: Simple per-cpu statistics count helper functions Date: Fri, 8 Apr 2016 12:16:19 -0400 Message-ID: <1460132182-11690-2-git-send-email-Waiman.Long@hpe.com> References: <1460132182-11690-1-git-send-email-Waiman.Long@hpe.com> Cc: linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, Scott J Norton , Douglas Hatch , Toshimitsu Kani , Waiman Long To: "Theodore Ts'o" , Andreas Dilger , Tejun Heo , Christoph Lameter Return-path: In-Reply-To: <1460132182-11690-1-git-send-email-Waiman.Long@hpe.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org This patch introduces a set of simple per-cpu statictics count helper functions that can be used by other kernel subsystems for keeping track of the number of events that happens. It is per-cpu based to reduce overhead and improve accuracy of the counter. Using per-cpu counter is usually overkill for such purpose. The following APIs are provided: - int percpu_stats_init(struct percpu_stats *pcs, int num) Initialize the per-cpu statictics counts structure which should have the given number of statistics counts. Return -ENOMEM on error. - void percpu_stats_destroy(struct percpu_stats *pcs) Free the percpu memory allocated. - void percpu_stats_inc(struct percpu_stats *pcs, int stat) void percpu_stats_dec(struct percpu_stats *pcs, int stat) void percpu_stats_add(struct percpu_stats *pcs, int stat, int cnt) Increment, decrement and add to the given per-cpu statistics count. - unsigned long percpu_stats_sum(struct percpu_stats *pcs, int stat) Return the current aggregated sum of the given statistics count. Signed-off-by: Waiman Long --- include/linux/percpu_stats.h | 42 +++++++++++++++++++++++++++ lib/Makefile | 2 +- lib/percpu_stats.c | 64 ++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 107 insertions(+), 1 deletions(-) create mode 100644 include/linux/percpu_stats.h create mode 100644 lib/percpu_stats.c diff --git a/include/linux/percpu_stats.h b/include/linux/percpu_stats.h new file mode 100644 index 0000000..ed6e8ac --- /dev/null +++ b/include/linux/percpu_stats.h @@ -0,0 +1,42 @@ +#ifndef _LINUX_PERCPU_STATS_H +#define _LINUX_PERCPU_STATS_H +/* + * Simple per-cpu statistics counts that have less overhead than the + * per-cpu counters. + */ +#include +#include + +struct percpu_stats { + unsigned long __percpu *stats; + int nstats; /* Number of statistics counts in stats array */ +}; + +extern void percpu_stats_destroy(struct percpu_stats *pcs); +extern int percpu_stats_init(struct percpu_stats *pcs, int num); +extern uint64_t percpu_stats_sum(struct percpu_stats *pcs, int stat); + +/** + * percpu_stats_add - Add the given value to a statistics count + * @pcs: Pointer to percpu_stats structure + * @stat: The statistics count that needs to be updated + * @cnt: The value to be added to the statistics count + */ +static inline void +percpu_stats_add(struct percpu_stats *pcs, int stat, int cnt) +{ + BUG_ON((unsigned int)stat >= pcs->nstats); + this_cpu_add(pcs->stats[stat], cnt); +} + +static inline void percpu_stats_inc(struct percpu_stats *pcs, int stat) +{ + percpu_stats_add(pcs, stat, 1); +} + +static inline void percpu_stats_dec(struct percpu_stats *pcs, int stat) +{ + percpu_stats_add(pcs, stat, -1); +} + +#endif /* _LINUX_PERCPU_STATS_H */ diff --git a/lib/Makefile b/lib/Makefile index 7bd6fd4..5037c62 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -40,7 +40,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \ gcd.o lcm.o list_sort.o uuid.o flex_array.o iov_iter.o clz_ctz.o \ bsearch.o find_bit.o llist.o memweight.o kfifo.o \ percpu-refcount.o percpu_ida.o rhashtable.o reciprocal_div.o \ - once.o + once.o percpu_stats.o obj-y += string_helpers.o obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o obj-y += hexdump.o diff --git a/lib/percpu_stats.c b/lib/percpu_stats.c new file mode 100644 index 0000000..bc9f26d --- /dev/null +++ b/lib/percpu_stats.c @@ -0,0 +1,64 @@ +/* + * Simple per-cpu statistics counts that have less overhead than the + * per-cpu counters. + */ +#include +#include + +/** + * percpu_stats_init - allocate memory for the percpu statistics counts + * @pcs: Pointer to percpu_stats structure + * @num: Number of statistics counts to be used + * Return: 0 if successful, -ENOMEM if memory allocation fails. + */ +int percpu_stats_init(struct percpu_stats *pcs, int num) +{ + int cpu; + + pcs->nstats = num; + pcs->stats = __alloc_percpu(sizeof(unsigned long) * num, + __alignof__(unsigned long)); + if (!pcs->stats) + return -ENOMEM; + + for_each_possible_cpu(cpu) { + unsigned long *pstats = per_cpu_ptr(pcs->stats, cpu); + int stat; + + for (stat = 0; stat < pcs->nstats; stat++, pstats++) + *pstats = 0; + } + return 0; +} +EXPORT_SYMBOL(percpu_stats_init); + +/** + * percpu_stats_destroy - free the memory used by the statistics counts + * @pcs: Pointer to percpu_stats structure + */ +void percpu_stats_destroy(struct percpu_stats *pcs) +{ + free_percpu(pcs->stats); + pcs->stats = NULL; + pcs->nstats = 0; +} +EXPORT_SYMBOL(percpu_stats_destroy); + +/** + * percpu_stats_sum - compute the percpu sum of the given statistics count + * @pcs : Pointer to percpu_stats structure + * @stat : The statistics count whose sum needs to be computed + * Return: Sum of percpu count values + */ +uint64_t percpu_stats_sum(struct percpu_stats *pcs, int stat) +{ + int cpu; + uint64_t sum = 0; + + BUG_ON((unsigned int)stat >= pcs->nstats); + + for_each_possible_cpu(cpu) + sum += per_cpu(pcs->stats[stat], cpu); + return sum; +} +EXPORT_SYMBOL(percpu_stats_sum); -- 1.7.1