linux-kernel - Re: What causes iowait other than waiting for i/o?

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Date:	Tue, 29 May 2007 12:57:05 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Bill Davidsen <davidsen@....com>
CC:	Linux Kernel mailing List <linux-kernel@...r.kernel.org>
Subject: Re: What causes iowait other than waiting for i/o?

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.

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