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RE: [Xen-devel] Setting dom0-cpus to 0 doesn't use all cpus asdocumented

To: "Ryan Harper" <ryanh@xxxxxxxxxx>, "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Subject: RE: [Xen-devel] Setting dom0-cpus to 0 doesn't use all cpus asdocumented
From: "Carb, Brian A" <Brian.Carb@xxxxxxxxxx>
Date: Tue, 9 May 2006 11:57:43 -0400
Cc: "Puthiyaparambil, Aravindh" <aravindh.puthiyaparambil@xxxxxxxxxx>, Xen-devel@xxxxxxxxxxxxxxxxxxx, "Krysan, Susan" <KRYSANS@xxxxxxxxxx>, "Subrahmanian, Raj" <raj.subrahmanian@xxxxxxxxxx>, "Vessey, Bruce A" <Bruce.Vessey@xxxxxxxxxx>
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Thread-topic: [Xen-devel] Setting dom0-cpus to 0 doesn't use all cpus asdocumented
We discovered this when running the xm-test suite. One of the tests
(01_enforce_dom0_cpus) changes the number of cpus by editing the
xend-config.sxp file and restarting xend. Should this test be updated to
use the method Ian suggested, to vary the number of cpus, rather than
restarting xend?

brian carb (610-648-2437 or N2 385-2437)
unisys cmp technology lab
malvern, pa

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-----Original Message-----
From: Ryan Harper [mailto:ryanh@xxxxxxxxxx] 
Sent: Tuesday, May 09, 2006 11:45 AM
To: Ian Pratt
Cc: Carb, Brian A; Xen-devel@xxxxxxxxxxxxxxxxxxx; Subrahmanian, Raj;
Krysan, Susan; Puthiyaparambil, Aravindh; Vessey, Bruce A
Subject: Re: [Xen-devel] Setting dom0-cpus to 0 doesn't use all cpus

* Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx> [2006-05-09 10:07]:
> > The comments for dom0-cpus in the xend-config.sxp file indicate that

> > setting this value to 0 in an SMP system will cause dom0 to use all 
> > the available CPUs. However, it appears as if setting this value to 
> > 0 does not change the number of CPUs at all.
> > 
> > I'm running SLES10 Beta 11 and xen-unstable changeset 9960 on a 
> > Unisys ES7000 with 32 CPUs and 32GB memory. In xend-config.sxp, 
> > dom0-cpus is set to 0. When xen dom0 boots, it is using all 32 procs

> > (as reported by 'grep processor /proc/cpuinfo | wc -l').
> > 
> > If I edit the xend-config.sxp file, change the value of dom0-cpus to

> > 1, and restart xend, dom0 correctly uses 1 CPUs.
> > If I then change dom0-cpus to 0 and restart xend, dom0 still uses 1 
> > cpu. The only way to have dom0 use 32 cpus again is to either set 
> > the value of dom0-cpus to 32, or reboot xen.
> > 
> > Has anyone else seen this behavior?
> You can just use the normal xm commands to vary the number of CPUs.
> Restarting xend is a rather brutal way of trying to achieve the same 
> thing...

Is it worth keeping dom0-cpus then?

Ryan Harper
Software Engineer; Linux Technology Center IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253

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