linux-kernel - Re: IO scheduler based IO controller V10

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Message-ID: <20091002171354.GH31616@kernel.dk>
Date:	Fri, 2 Oct 2009 19:13:54 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Ray Lee <ray-lk@...rabbit.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Mike Galbraith <efault@....de>,
	Vivek Goyal <vgoyal@...hat.com>,
	Ulrich Lukas <stellplatz-nr.13a@...enparkplatz.de>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
	mikew@...gle.com, fchecconi@...il.com, paolo.valente@...more.it,
	ryov@...inux.co.jp, fernando@....ntt.co.jp, jmoyer@...hat.com,
	dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	righi.andrea@...il.com, m-ikeda@...jp.nec.com, agk@...hat.com,
	akpm@...ux-foundation.org, peterz@...radead.org,
	jmarchan@...hat.com, riel@...hat.com
Subject: Re: IO scheduler based IO controller V10

On Fri, Oct 02 2009, Ray Lee wrote:
> On Fri, Oct 2, 2009 at 7:56 AM, Jens Axboe <jens.axboe@...cle.com> wrote:
> > In some cases I wish we had a server vs desktop switch, since it would
> > decisions on this easier. I know you say that servers care about
> > latency, but not at all to the extent that desktops do. Most desktop
> > users would gladly give away the top of the performance for latency,
> > that's not true of most server users. Depends on what the server does,
> > of course.
> 
> If most of the I/O on a system exhibits seeky tendencies, couldn't the
> schedulers notice that and use that as the hint for what to optimize?
> 
> I mean, there's no switch better than the actual I/O behavior itself.

Heuristics like that have a tendency to fail. What's the cut-off point?
Additionally, heuristics based on past process/system behaviour also has
a tendency to be suboptimal, since things aren't static.

We already look at seekiness of individual processes or groups. IIRC,
as-iosched also keeps a per-queue tracking.

-- 
Jens Axboe

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