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

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Date:	Fri, 2 Oct 2009 11:24:09 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	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, torvalds@...ux-foundation.org, riel@...hat.com
Subject: Re: IO scheduler based IO controller V10


* Jens Axboe <jens.axboe@...cle.com> wrote:

> It's not hard to make the latency good, the hard bit is making sure we 
> also perform well for all other scenarios.

Looking at the numbers from Mike:

 | dd competing against perf stat -- konsole -e exec timings, 5 back to 
 | back runs
 |                                                         Avg
 | before         9.15    14.51     9.39    15.06     9.90   11.6
 | after [+patch] 1.76     1.54     1.93     1.88     1.56    1.7

_PLEASE_ make read latencies this good - the numbers are _vastly_ 
better. We'll worry about the 'other' things _after_ we've reached good 
latencies.

I thought this principle was a well established basic rule of Linux IO 
scheduling. Why do we have to have a 'latency vs. bandwidth' discussion 
again and again? I thought latency won hands down.

	Ingo
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