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

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Date:	Fri, 2 Oct 2009 18:37:07 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Galbraith <efault@....de>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	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


* Mike Galbraith <efault@....de> wrote:

> On Fri, 2009-10-02 at 11:24 +0200, Ingo Molnar wrote:
> > * 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.
> 
> Just a note: In the testing I've done so far, we're better off today 
> than ever, [...]

Definitely so, and a couple of months ago i've sung praises of that 
progress on the IO/fs latencies front:

   http://lkml.org/lkml/2009/4/9/461

... but we are greedy bastards and dont define excellence by how far 
down we have come from but by how high we can still climb ;-)

	Ingo
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