Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765418AbXE2UBS (ORCPT ); Tue, 29 May 2007 16:01:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758511AbXE2UBJ (ORCPT ); Tue, 29 May 2007 16:01:09 -0400 Received: from mail.tmr.com ([64.65.253.246]:33563 "EHLO gaimboi.tmr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757949AbXE2UBI (ORCPT ); Tue, 29 May 2007 16:01:08 -0400 Message-ID: <465C8684.2030600@tmr.com> Date: Tue, 29 May 2007 16:01:08 -0400 From: Bill Davidsen User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.8) Gecko/20061105 SeaMonkey/1.0.6 MIME-Version: 1.0 To: Rik van Riel CC: Linux Kernel mailing List Subject: Re: What causes iowait other than waiting for i/o? References: <465B4B75.2040602@tmr.com> <465C5B61.6000702@redhat.com> In-Reply-To: <465C5B61.6000702@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1898 Lines: 42 Rik van Riel wrote: > 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. > > All filesystem IO and direct disk IO can cause iowait. > > This includes NFS activity. > If I didn't note it before, I'm read the the data from /proc, cpustats, net/dev, and diskstats. I assume that all i/o would show up in one of those places. NFS isn't involved, although this machine is a fileserver as a side job the modules weren't even loaded during testing. A puzzlement for future consideration. If I get a chance later this week I'll make a pretty graphic of all the stuff going on when the iowait spiked, ctx rate, inq rate, hell the last time I even grabbed the CPU temp to see if it told me anything (didn't, thermal throttling NOT). Thanks for the feedback, I think that lets out the obvious stuff. -- Bill Davidsen "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot - 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/