From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932976AbYB2PrY (ORCPT ); Fri, 29 Feb 2008 10:47:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758170AbYB2PrN (ORCPT ); Fri, 29 Feb 2008 10:47:13 -0500 Received: from nf-out-0910.google.com ([64.233.182.190]:32509 "EHLO nf-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754793AbYB2PrM (ORCPT ); Fri, 29 Feb 2008 10:47:12 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; b=NlUp/c8XcdAQ3vaV8zjh1R5YicxGy9h8KWi8AcvwhUGi1JaEauc6cTiR292WKPlR2NdBvLutmczbg8n367iwwjVK5/4v2XJ9K9jTfcTeMD0Y+IyfsffA+7KUqFqPYhGwv38h7OGOERv1Rd5YqVp6EHK3ufL3P5Tjlwtip0kpIjk= Message-ID: <74d8fc520802290747o2c97992ar7af2b8c295fe2fb2@mail.gmail.com> Date: Fri, 29 Feb 2008 15:47:08 +0000 From: "Gordon Mckeown" To: LKML Subject: Re: Very high IOWait during all disk activity Cc: "Tomasz Chmielewski" In-Reply-To: <47C82244.60307@wpkg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <47C82244.60307@wpkg.org> X-Google-Sender-Auth: 8697a231fa31572a Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 29, 2008 at 3:18 PM, Tomasz Chmielewski wrote: > Unless you can write to the disk faster than fetch data from /dev/zero - > yes, it is normal. OK, thank you; it has been a struggle to get confirmation of this; perhaps because the way IOWait is measured has changed at some point? > Try running: > > cat /dev/zero | bzip2 -c >/dev/null > > when your IOwait is big (because you write a big file), and then watch > the numbers. Ah, I can see that the CPU-intensive command soaks up the cycles that would otherwise have been reported as IOWaits. Unfortunately this doesn't help explain why Windows XP on the same box can complete an "identical" copy operation in half the time. Perhaps it's just due to the different filesystems, or the way write caching works? Thanks, Gordon.