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

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Date:	Mon, 28 May 2007 17:36:53 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Linux Kernel mailing List <linux-kernel@...r.kernel.org>
Subject: What causes iowait other than waiting for i/o?

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.

-- 
bill davidsen <davidsen@....com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979

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