linux-kernel - Re: [patch V3] percpu_counter: scalability works

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Date:	Tue, 17 May 2011 08:55:33 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Tejun Heo <tj@...nel.org>
cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Shaohua Li <shaohua.li@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"npiggin@...nel.dk" <npiggin@...nel.dk>
Subject: Re: [patch V3] percpu_counter: scalability works

On Tue, 17 May 2011, Tejun Heo wrote:

> Hello,
>
> On Tue, May 17, 2011 at 03:00:23PM +0200, Eric Dumazet wrote:
> > Absolutely not. Its slow path yes, but not super-slow.
>
> I was speaking in relative terms.  We're talking about local only fast
> path vs. something which hits every percpu counter likely causing
> cache misses in many of them.  It's bound to be multiple orders of
> magnitude heavier than fast path.

Well lets just adopt the system that vm statistics use. Bound the error by
time and batch and allow the user to change the batch if more accuracy is
desired.

The _sum function is optional and should it should be explained that the
result *could* be better but dont count on it.

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