linux-kernel - Re: Help Resource Counters Scale Better (v3)

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Date:	Mon, 10 Aug 2009 15:22:05 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	balbir@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	andi.kleen@...el.com, Prarit Bhargava <prarit@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
	"menage@...gle.com" <menage@...gle.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: Help Resource Counters Scale Better (v3)

On Mon, 10 Aug 2009 14:45:59 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> > Do you agree?
> 
> Ok. Config is enough at this stage.
> 
> The last advice for merge is, it's better to show the numbers or
> ask someone who have many cpus to measure benefits. Then, Andrew can
> know how this is benefical.
> (My box has 8 cpus. But maybe your IBM collaegue has some bigger one)
> 
> In my experience (in my own old trial),
>  - lock contention itself is low. not high.
>  - but cacheline-miss, pingpong is very very frequent.
> 
> Then, this patch has some benefit logically but, in general,
> File-I/O, swapin-swapout, page-allocation/initalize etc..dominates
> the performance of usual apps. You'll have to be careful to select apps
> to measure the benfits of this patch by application performance.
> (And this is why I don't feel so much emergency as you do)
> 

Why I say "I want to see the numbers" again and again is that
this is performance improvement with _bad side effect_.
If this is an emergent trouble, and need fast-track, which requires us
"fix small problems later", plz say so. 

I have no objection to this approach itself because I can't think of
something better, now. percpu-counter's error tolerance is a generic
problem and we'll have to visit this anyway.

Thanks,
-Kame

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