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SubjectRe: ext3 IO latency measurements (was: Linux 2.6.29)
On Thu, 26 Mar 2009 15:36:18 +0100
Jens Axboe <jens.axboe@oracle.com> wrote:

> On Thu, Mar 26 2009, Arjan van de Ven wrote:
> > On Thu, 26 Mar 2009 12:08:15 +0100
> > Jens Axboe <jens.axboe@oracle.com> wrote:
> > >
> > > Did you capture the trace of the long delays in the read test
> > > case? It can be two things, at least. One is that each little
> > > read takes much longer than it should, the other is that we get
> > > stuck waiting on a dirty page and hence that slows down the reads
> > > a lot.
> > >
> >
> > would be interesting to run latencytop during such runs...
>
> Things just drown in the noise in there sometimes, is my experience...
> And disappear. Perhaps I'm just not very good at reading the output,
> but it was never very useful for me. I know, not a very useful
> complaint, I'll try and use it again and come up with something more
> productive :-)
>
> But in this case, I bet it's also the atime updates. If Ingo turned
> those off, the read results would likely be a lot better (and
> consistent).

latencytop does identify those for sure.
>


--
Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,
visit http://www.lesswatts.org


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