From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dario Faggioli <dario.faggioli@citrix.com>
Subject: Re: CAP and performance problem
Date: Tue, 21 May 2013 15:06:16 +0200
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To: Massimo Canonico <mex@di.unipmn.it>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
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On mar, 2013-05-21 at 13:54 +0200, Massimo Canonico wrote:
> Hi George,
> thanks for your answer.
>=20
> Our physical machine has two processors and two cores for each processors=
.
>=20
> The virtual machine where our application run has just one VCPU that is=
=20
> pinned to a single core.
> Instead, dom0 was not pinned to any particular core.
>=20
Ok, and what are you doing in Dom0? I guess almost nothing, is that the
case?

Also, when inspecting the vCPU utilization, do you see the VM vCPU busy
up to 100% without cap (or with cap set to 100) and, OTOH, up to 50%
with cap set to 50?

> So I think that my problem could not be related to the presence of 4 vcpu=
s.
>=20
Well, looks like a scheduling issue, or, in any case, one where
something is interacting with the scheduling. Can you perhaps boot Dom0
so that it uses only 2 or 3 cores (or arrange for that later, e.g., with
cpupools) and pin the vCPU of the VM on the 4th one?

I'm not sure what could be going on, but that sounds a reasonable way to
rule out as much room for interference as possible...

Dario

--=20
<<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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