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Say I have a Dual-Core server, that's 4 cores w/ two physical processors.

I read numerous articles that states the dom0 should get one physical core to itself. By core, does that mean a single CPU core or one of the 4 logical cores? Ideally I would like to dedicate a single CPU core (2 logical) to the dom0. Then I would give the other CPU split between the 3 VMs. I've seen examples where ppl would assign more than the available number of cores to a VM and I don't know what good that would do. I mean, why would I want to assign 4 vCPU to a single VM when I only have 2 available (if my math is correct)? I assume I only have 2 available from the one core as I've given dom0 a CPU to itself.

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They mean a core in that instance. So give it one of the four logical cores. The rest can be used for DomUs. As for oversubscribing vCPUs to VM's know your workload. If your VMs are likely to be idle most of the time, then oversubscribing a fair ways is quite doable. If they're going to be busy, then a 1:1 core to vcpu is more advisable.

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  • So when I pin a vCPU to a core, I'm really pinning it to one of the four logical cores? Since I only have 2 physical CPUs, I thought I was only able to pin it to one of two.
    – sdot257
    Jun 29, 2011 at 12:00
  • That is correct. Pinning a vCPU pins it to an execution core, not a socket.
    – sysadmin1138 ♦
    Jun 29, 2011 at 14:09

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