linux-ext4 - Re: regression: 100% io-wait with 2.6.24-rcX

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Date:	Sat, 19 Jan 2008 02:24:15 -0800 (PST)
From:	Martin Knoblauch <spamtrap@...bisoft.de>
To:	Mike Snitzer <snitzer@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mel Gorman <mel@....ul.ie>, Fengguang Wu <wfg@...l.ustc.edu.cn>,
	Peter Zijlstra <peterz@...radead.org>, jplatte@...sa.net,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	James.Bottomley@...eleye.com
Subject: Re: regression: 100% io-wait with 2.6.24-rcX

----- Original Message ----
> From: Mike Snitzer <snitzer@...il.com>
> To: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Mel Gorman <mel@....ul.ie>; Martin Knoblauch <spamtrap@...bisoft.de>; Fengguang Wu <wfg@...l.ustc.edu.cn>; Peter Zijlstra <peterz@...radead.org>; jplatte@...sa.net; Ingo Molnar <mingo@...e.hu>; linux-kernel@...r.kernel.org; "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>; James.Bottomley@...eleye.com
> Sent: Friday, January 18, 2008 11:47:02 PM
> Subject: Re: regression: 100% io-wait with 2.6.24-rcX
> 
> > I can fire up 2.6.24-rc8 in short order to see if things are vastly
> > improved (as Martin seems to indicate that he is happy with
> > AACRAID on 2.6.24-rc8).  Although even Martin's AACRAID
> > numbers from 2.6.19.2
> 
 > are still quite good (relative to mine).  Martin can you share any tuning
> > you may have done to get AACRAID to where it is for you right now?
Mike,

 I have always been happy with the AACRAID box compared to the CCISS system. Even with the "regression" in 2.6.24-rc1..rc5 it was more than acceptable to me. For me the differences between 2.6.19  and 2.6.24-rc8 on the AACRAID setup are:

- 11% (single stream) to 25% (dual/triple stream) regression in DIO. Something I do not care much about. I just measure it for reference.
+ the very nice behaviour when writing to different targets (mix3), which I attribute to Peter's per-dbi stuff.

 And until -rc6 I was extremely pleased with the cool speedup I saw on my CCISS boxes. This would have been the next "production" kernel for me. But lets discuss this under a seperate topic. It has nothing to do with the original wait-io issue.

 Oh, before I forget. There has been no tuning for the AACRAID. The system is an IBM x3650 with built in AACRAID and battery backed write cache. The disks are 6x142GB/15krpm in a RAID5 setup. I see one big difference between your an my tests. I do 1MB writes to simulate the behaviour of the real applications, while yours seem to be much smaller.

Cheers
Martin

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