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

[Waiman Long]

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