From: Linus Torvalds Subject: Re: regression: 100% io-wait with 2.6.24-rcX Date: Fri, 18 Jan 2008 11:23:15 -0800 (PST) Message-ID: References: <903015.63912.qm@web32611.mail.mud.yahoo.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: 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 To: Martin Knoblauch Return-path: Received: from smtp2.linux-foundation.org ([207.189.120.14]:47031 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758982AbYARTYI (ORCPT ); Fri, 18 Jan 2008 14:24:08 -0500 In-Reply-To: <903015.63912.qm@web32611.mail.mud.yahoo.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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