Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932598AbXE1Vr4 (ORCPT ); Mon, 28 May 2007 17:47:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751498AbXE1Vrt (ORCPT ); Mon, 28 May 2007 17:47:49 -0400 Received: from wa-out-1112.google.com ([209.85.146.179]:19266 "EHLO wa-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750852AbXE1Vrt (ORCPT ); Mon, 28 May 2007 17:47:49 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=rtu6emG7RZEIJ/3Q97hCdsA1fNNksOmXbbu0Ad/hsFWawCm9UZdubR9uIKSm++iAkxwQzSEhJ7PPtBq11sSZytAyoSpjnhSHiVxGRTieicxXEBxeV93u9txm3AKvD38WEwRjd/f8qQ0GP4/U5PuK+IbvxB015yz8fG4r9y5R/mk= Message-ID: <9a8748490705281447t24a263a0hd5946825d3f486c7@mail.gmail.com> Date: Mon, 28 May 2007 23:47:48 +0200 From: "Jesper Juhl" To: "Bill Davidsen" Subject: Re: What causes iowait other than waiting for i/o? Cc: "Linux Kernel mailing List" In-Reply-To: <465B4B75.2040602@tmr.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <465B4B75.2040602@tmr.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1763 Lines: 35 On 28/05/07, Bill Davidsen wrote: > I recently noted that my system was spending a lot of time in i/o wait > when doing some tasks which I thought didn't involve i/o, as noted by > the lack of disk light activity most of the time. I thought of network, > certainly the NIC had no activity for this job. So I set up a little > loop to capture all disk i/o and network activity (including loopback). > That was no obvious help, and the program doesn't use pipes. > > At this point I'm really curious, does someone have a good clue? > > Note: I don't think this is a bug or performance issue, unless the > kernel is doing something and charging time to iowait instead of system > I don't see anything to fix, but I would like to understand. > Nothing /should/ cause time to be attributed to i/o wait other than waiting for i/o. But the accounting isn't completely accurate. When the kernel records what the has happen (governed by when the timer interrupt triggers as far as I remember), many different processes may have run and done may different things, but only what the last one did is recorded. So if you are unlucky you may have the system doing all sorts of activities, but only recording i/o wait if the last process to run before the kernel looked was doing i/o wait... The numbers are not exactely accurate... -- Jesper Juhl Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html Plain text mails only, please http://www.expita.com/nomime.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/