Re: [Xen-devel] Delays on usleep calls

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On gio, 2014-01-23 at 21:09 +0200, Pavlo Suikov wrote:
> Hi Dario,
> 
> > Can I ask how the numbers (for DomU, of course) looks like now?
> 
> 
> They are all 31 ms, so minimal overhead is achieved. However, it looks
> like we still have some gremlins in there: from boot to boot this time
> can change to 39 ms. So without Xen scheduler being active sleep
> latency stabilizes, but not always on a correct value.
> 
Wow... So, you're saying that, with the DomU exclusively pinned to a
specific pCPU, latency is stable, but the value at which it stabilizes
varies from boot to boot?

That's very weird...

> > Another thing I'll try, if you haven't done that already, is as
> follows:
> > - get rid of the DomU
> > - pin the 2 Dom0's vCPUs each one to one pCPU
> > - repeat the experiment
> 
> 
> Yeah, we have tried this as well and it gives us almost the same
> result as in previous case: sleep latency in dom0 is not present, so
> we get 30 to 31 ms on 30 ms sleep without any variations.
> 
Ok. Are you aware of xentrace and xenalyze?

Have, for example, a look here:
http://blog.xen.org/index.php/2012/09/27/tracing-with-xentrace-and-xenalyze/

Perhaps you could, in this Dom0 case, you can start the tracing, start
the DomU and then run the experiments. It's going to be though to
correlate the actual activity in Dom0 (the test running inside it), with
the Xen's traces, but at least you should be able to see when, and try
to figure out why, the DomU, which should be just idle, ends up getting
in your way.

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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