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

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Message-ID: <20090810074134.GA4648@balbir.in.ibm.com>
Date:	Mon, 10 Aug 2009 13:11:34 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	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)

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-08-10 15:22:05]:

> 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. 
> 


Yes, this is an emergent trouble, I've gotten reports of the lock
showing up on 16 to 64 ways.

> 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.
>

Yes, my plan is to then later add a strict/no-strict accounting layer
and allow users to choose. Keep root as non-script as we don't
support limit setting on root now. 

-- 
	Balbir
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