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Re: [Xen-users] More vcpus than physical cores and hvm

To: "Alexandre Biancalana" <biancalana@xxxxxxxxx>
Subject: Re: [Xen-users] More vcpus than physical cores and hvm
From: "Javier Guerra" <javier@xxxxxxxxxxx>
Date: Wed, 24 Sep 2008 16:43:23 -0500
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On Wed, Sep 24, 2008 at 4:32 PM, Alexandre Biancalana
<biancalana@xxxxxxxxx> wrote:
> Can I have more vcpus than physical cores on Xen ??

sure, if you count Dom0, you already had more vcpus than cores.

i'd guess that what you're seeing is not a problem; but a limitation
of language.

imagine an extreme case, machine with few cores and many DomU's.  the
hypervisor CPU scheduler would assign a fraction of CPU to each DomU,
so they run slower.  in these conditions nobody would be surprised
that even light loads can go to 100% cpu use.

your case is nowhere extreme; but similar. before you had unused
capacity; but it was assigned to the DomU's, so they report only 70%
use.  when you start using that extra capacity, the 'old' DomU's get a
smaller slice, so they use a bigger percentage of that smaller slice.


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