linux-kernel - Re: Do not overload dispatch queue (Was: Re: IO scheduler based IO controller V10)

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Message-Id: <1254597074.7153.12.camel@marge.simson.net>
Date:	Sat, 03 Oct 2009 21:11:14 +0200
From:	Mike Galbraith <efault@....de>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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: Do not overload dispatch queue (Was: Re: IO scheduler based IO
 controller V10)

On Sat, 2009-10-03 at 21:07 +0200, Mike Galbraith wrote:
> On Sat, 2009-10-03 at 19:35 +0200, Jens Axboe wrote:

> > So that's pure goodness, at least.
> 
> Yeah, but it's a double edged sword, _maybe_ cut too far in the other
> direction.  (impression)
> 
> > > perf stat testo.sh                               Avg
> > > 108.12   106.33    106.34    97.00    106.52   104.8  1.000 fairness=0 overload_delay=0
> > >  93.98   102.44     94.47    97.70     98.90    97.4   .929 fairness=0 overload_delay=1
> > >  90.87    95.40     95.79    93.09     94.25    93.8   .895 fairness=1 overload_delay=0
> > >  89.93    90.57     89.13    93.43     93.72    91.3   .871 fairness=1 overload_delay=1
> > >  89.81    88.82     91.56    96.57     89.38    91.2   .870 desktop=1 +last_end_sync
> > >  92.61    94.60     92.35    93.17     94.05    93.3   .890 block-for-linus
> > 
> > Doesn't look too bad, all things considered. Apart from "stock" cfq,
> > it's consistent. And being consistent is a Good Thing. Performance wise,
> > it's losing out to "stock" but looks pretty competetive otherwise.
> 
> No, not bad at all, still a large win over stock.
> 
> > So far that looks like a winner. The dictator wanted good latency, he's
> > getting good latency. I'll continue working on this on monday, while I'm
> > waiting for delivery of the Trabant.
> 
> I'm unsure feel wise.  Disk is sounding too seeky, which worries me.

But, this is a _huge_ improvement of the dd vs reader thing regardless
of any further tweaking that may or may not prove necessary.  That ages
old corner case seems to be defeated.

	-Mike

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