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

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Date:	Tue, 22 Jan 2008 14:39:33 +0000
From:	Alasdair G Kergon <agk@...hat.com>
To:	Martin Knoblauch <spamtrap@...bisoft.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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, Jens Axboe <jens.axboe@...cle.com>,
	Milan Broz <mbroz@...hat.com>, Neil Brown <neilb@...e.de>
Subject: Re: regression: 100% io-wait with 2.6.24-rcX

On Fri, Jan 18, 2008 at 11:01:11AM -0800, Martin Knoblauch wrote:
>  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. 

What is your LVM device configuration?
  E.g. 'dmsetup table' and 'dmsetup info -c' output.
Some configurations lead to large IOs getting split up on the way through
device-mapper.

See if these patches make any difference:
  http://www.kernel.org/pub/linux/kernel/people/agk/patches/2.6/editing/

    dm-md-merge_bvec_fn-with-separate-bdev-and-sector.patch
    dm-introduce-merge_bvec_fn.patch
    dm-linear-add-merge.patch
    dm-table-remove-merge_bvec-sector-restriction.patch
 
Alasdair
-- 
agk@...hat.com
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