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

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Date:	Fri, 02 Oct 2009 16:45:42 +0200
From:	Mike Galbraith <efault@....de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Jens Axboe <jens.axboe@...cle.com>, Ingo Molnar <mingo@...e.hu>,
	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, 2009-10-02 at 07:24 -0700, Linus Torvalds wrote:
> 
> On Fri, 2 Oct 2009, Jens Axboe wrote:
> > 
> > It's really not that simple, if we go and do easy latency bits, then
> > throughput drops 30% or more.
> 
> Well, if we're talking 500-950% improvement vs 30% deprovement, I think 
> it's pretty clear, though. Even the server people do care about latencies. 
> 
> Often they care quite a bit, in fact.
> 
> And Mike's patch didn't look big or complicated.

But it is a hack.  (thought about and measured, but hack nonetheless)

I haven't tested it on much other than reader vs streaming writer.  It
may well destroy the rest of the IO universe. I don't have the hw to
even test any hairy chested IO.

	-Mike

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