Re: [PATCH 1/2] Make the batch size of the percpu_counterconfigurable

[Eric Dumazet]

On Tue, 2013-04-30 at 09:23 -0700, Tim Chen wrote:
> On Tue, 2013-04-30 at 13:32 +0000, Christoph Lameter wrote:
> > On Mon, 29 Apr 2013, Tim Chen wrote:
> > 
> > > diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
> > > index d5dd465..5ca7df5 100644
> > > --- a/include/linux/percpu_counter.h
> > > +++ b/include/linux/percpu_counter.h
> > > @@ -22,6 +22,7 @@ struct percpu_counter {
> > >  	struct list_head list;	/* All percpu_counters are on a list */
> > >  #endif
> > >  	s32 __percpu *counters;
> > > +	int *batch ____cacheline_aligned_in_smp;
> > >  };
> > 
> > What is this for and why does it have that alignmend?
> 
> I was assuming that if batch is frequently referenced, it probably
> should not share a cache line with the counters field.

But 'counters' field has the same requirement. Its supposed to be read
only field. 

So please remove this '____cacheline_aligned_in_smp', as it makes the
whole struct percpu_counter at least two cache lines wide, for no
obvious reason.




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