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

[Nikolay Borisov]

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.