Re: [PATCH 2/3] percpu_stats: Simple per-cpu statistics count helper functions

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On 04/04/2016 03:36 AM, Nikolay Borisov wrote:

On 04/02/2016 06:09 AM, Waiman Long wrote:
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<Waiman.Long@xxxxxxx>
---
  include/linux/percpu_stats.h |  103 ++++++++++++++++++++++++++++++++++++++++++
  1 files changed, 103 insertions(+), 0 deletions(-)
  create mode 100644 include/linux/percpu_stats.h
Just one minor nit below.
[..]
+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();
+}
pstat = get_cpu_ptr(&pcs->stats[stat]);
*pstat += cnt;
put_cpu_ptr(&pcs->stats[stat]);

It will generate identical code but this one uses APIs, making the
intention clearer. But as I said this is just a minor nit.

you can add my Reviewed-by: Nikolay Borisov<kernel@xxxxxxxx>  for this
particular patch.

Yes, that will certainly make it look nicer. I will update the patch once I get feedback from my other ext4 patches.

Cheers,
Longman
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