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

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Date:	Fri, 18 Jan 2008 11:23:15 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Martin Knoblauch <spamtrap@...bisoft.de>
cc:	Mel Gorman <mel@....ul.ie>, Fengguang Wu <wfg@...l.ustc.edu.cn>,
	Mike Snitzer <snitzer@...il.com>,
	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



On Fri, 18 Jan 2008, Martin Knoblauch wrote:
>
>  just to make one thing clear - I am not so much concerned about the
> performance of AACRAID. It is OK with or without Mel's patch. It is
> better with Mel's patch. The regression in DIO compared to 2.6.19.2 is
> completely independent of Mel's stuff.
> 
>  What interests me much more is the behaviour of the CCISS+LVM based
> system. Here I see a huge benefit of reverting Mel's patch.

Ok, I just got your usage cases confused.

The argument stays the same: some controllers/drivers may have subtle 
behavioural differences that come from the IO limits themselves.

So it wasn't AACRAID, it was CCISS+LVM. The argument is the same: it may 
well be that the *bigger* IO sizes are actually what hurts, even if the 
conventional wisdom is traditionally that bigger submissions are better.

>  At least, rc1-rc5 have shown that the CCISS system can do well. Now
> the question is which part of the system does not cope well with the
> larger IO sizes? Is it the CCISS controller, LVM or both. I am open to
> suggestions on how to debug that. 

I think you need to ask the MD/DM people for suggestions.. Who aren't cc'd 
here.

		Linus
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