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

[Bill Davidsen <davidsen@tmr.com>]

Satyam Sharma wrote:
> Hi Bill,
>
> On 5/29/07, Bill Davidsen <davidsen@tmr.com> 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.
>
> What tool / kernel instrumentation / mechanism are you using to
> determine that some task(s) are indeed blocked waiting for i/o? Perhaps
> some userspace process accounting tools could be "broken" in the sense
> that they generalize all uninterruptible sleep as waiting for i/o ...

I wouldn't expect /proc/stat and similar to be broken in that way, but 
If no one has a better idea I guess I will assume there's a check needed 
of where time is added to iowait. I was hoping to avoid a full kernel 
search. Never thought of /proc data as a user space tool, but I guess.

--
Bill Davidsen <davidsen@tmr.com>
 "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

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