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

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Date:	Sat, 03 Oct 2009 11:00:34 +0200
From:	Mike Galbraith <efault@....de>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 Sat, 2009-10-03 at 09:24 +0200, Jens Axboe wrote:

> After shutting down the computer yesterday, I was thinking a bit about
> this issue and how to solve it without incurring too much delay. If we
> add a stricter control of the depth, that may help. So instead of
> allowing up to max_quantum (or larger) depths, only allow gradual build
> up of that the farther we get away from a dispatch from the sync IO
> queues. For example, when switching to an async or seeky sync queue,
> initially allow just 1 in flight. For the next round, if there still
> hasn't been sync activity, allow 2, then 4, etc. If we see sync IO queue
> again, immediately drop to 1.
> 
> It could tie in with (or partly replace) the overload feature. The key
> to good latency and decent throughput is knowing when to allow queue
> build up and when not to.

Hm.  Starting at 1 sounds a bit thin (like IDLE), multiple iterations to
build/unleash any sizable IO, but that's just my gut talking.

	-Mike

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