From: Alasdair G Kergon Subject: Re: regression: 100% io-wait with 2.6.24-rcX Date: Tue, 22 Jan 2008 14:39:33 +0000 Message-ID: <20080122143933.GA11111@agk.fab.redhat.com> References: <903015.63912.qm@web32611.mail.mud.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Linus Torvalds , Mel Gorman , Fengguang Wu , Mike Snitzer , Peter Zijlstra , jplatte@naasa.net, Ingo Molnar , linux-kernel@vger.kernel.org, "linux-ext4@vger.kernel.org" , James.Bottomley@steeleye.com, Jens Axboe , Milan Broz , Neil Brown To: Martin Knoblauch Return-path: Received: from mx1.redhat.com ([66.187.233.31]:37540 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752518AbYAVOlJ (ORCPT ); Tue, 22 Jan 2008 09:41:09 -0500 Content-Disposition: inline In-Reply-To: <903015.63912.qm@web32611.mail.mud.yahoo.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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@redhat.com