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[Xen-users] Re: [Xen-devel] dom0-cpus problem with Xen 3.4.1-rc6

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: [Xen-users] Re: [Xen-devel] dom0-cpus problem with Xen 3.4.1-rc6
From: Pasi Kärkkäinen <pasik@xxxxxx>
Date: Wed, 22 Jul 2009 20:29:06 +0300
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "xen-users@xxxxxxxxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxxxxxxxx>, Nerijus Narmontas <n.narmontas@xxxxxxxxx>
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On Wed, Jul 22, 2009 at 06:15:05PM +0100, Keir Fraser wrote:
> On 22/07/2009 18:01, "Pasi Kärkkäinen" <pasik@xxxxxx> wrote:
> >> Can you tell me what's the difference between Xen boot
> >> option dom0_max_vcpus=1 and (dom0-cpus 1) option
> >> in /etc/xen/xend-config.sxp?
> > 
> > If I haven't misunderstood this dom0-cpus option in xend-config.sxp tells
> > which physical CPUs/cores vcpu's of dom0 will use..
> > 
> > ie. if you limit dom0_max_vcpus=1, then you can use dom0-cpus to tell which
> > one of the 8 available cpus/cores dom0's 1 vcpu will run on.
> dom0-cpus does the same as dom0_max_vcpus -- it specifies number of VCPUs
> which dom0 should run with. The difference is that dom0_max_vcpus=1 means
> that is all that dom0 kernel will detect and boot with: you cannot
> subsequently enable more. With (dom0-cpus 1), dom0 will boot with a vcpu for
> every host cpu (by default) and then hot-unplug/offline all but one vcpu
> when xend starts. The latter is obviously a more complex operation, but
> could be reverted (i.e., you could online some of those vcpus at a later
> time).

Hmm, so 'dom0-cpus' in xend-config.sxp doesn't limit on what physical CPUs
the VCPUs of dom0 can run on?

Then many people have gotten that wrong.. :)

-- Pasi

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