From: Waiman Long Subject: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper functions Date: Fri, 1 Apr 2016 23:09:37 -0400 Message-ID: <1459566578-30221-3-git-send-email-Waiman.Long@hpe.com> References: <1459566578-30221-1-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: <1459566578-30221-1-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) Increment and decrement 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. - void percpu_stats_reset(struct percpu_stats *pcs) Clear all the statistics counts defined in the given percpu_stats structure. Signed-off-by: Waiman Long --- include/linux/percpu_stats.h | 103 ++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 103 insertions(+), 0 deletions(-) create mode 100644 include/linux/percpu_stats.h diff --git a/include/linux/percpu_stats.h b/include/linux/percpu_stats.h new file mode 100644 index 0000000..a4f715e --- /dev/null +++ b/include/linux/percpu_stats.h @@ -0,0 +1,103 @@ +#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 */ +}; + +/* + * Reset the all statistics counts to 0 in the percpu_stats structure + */ +static inline void percpu_stats_reset(struct percpu_stats *pcs) +{ + int cpu; + + 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; + } + + /* + * If a statistics count is in the middle of being updated, it + * is possible that the above clearing may not work. So we need + * to double check again to make sure that the counters are really + * cleared. Still there is a still a very small chance that the + * second clearing does not work. + */ + for_each_possible_cpu(cpu) { + unsigned long *pstats = per_cpu_ptr(pcs->stats, cpu); + int stat; + + for (stat = 0; stat < pcs->nstats; stat++, pstats++) + if (*pstats) + *pstats = 0; + } +} + +static inline int percpu_stats_init(struct percpu_stats *pcs, int num) +{ + pcs->nstats = num; + pcs->stats = __alloc_percpu(sizeof(unsigned long) * num, + __alignof__(unsigned long)); + if (!pcs->stats) + return -ENOMEM; + + percpu_stats_reset(pcs); + return 0; +} + +static inline void percpu_stats_destroy(struct percpu_stats *pcs) +{ + free_percpu(pcs->stats); + pcs->stats = NULL; + pcs->nstats = 0; +} + +static inline void +__percpu_stats_add(struct percpu_stats *pcs, int stat, int cnt) +{ + unsigned long *pstat; + + if ((unsigned int)stat >= pcs->nstats) + return; + preempt_disable(); + pstat = this_cpu_ptr(&pcs->stats[stat]); + *pstat += cnt; + preempt_enable(); +} + +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); +} + +static inline unsigned long +percpu_stats_sum(struct percpu_stats *pcs, int stat) +{ + int cpu; + unsigned long sum = 0; + + if ((unsigned int)stat >= pcs->nstats) + return sum; + + for_each_possible_cpu(cpu) + sum += per_cpu(pcs->stats[stat], cpu); + return sum; +} + +#endif /* _LINUX_PERCPU_STATS_H */ -- 1.7.1