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Re: [libvirt] [PATCH] qemu: Remove limit enforcing when setting processor count

On 09/07/2012 09:13 AM, Daniel P. Berrange wrote:
> On Fri, Sep 07, 2012 at 02:51:00PM +0200, Peter Krempa wrote:
>> When setting processor count for a domain using the API libvirt enforced
>> a maximum processor count that was determined using an IOCTL on
>> /dev/kvm. Unfortunately this value isn't representative enough and qemu
>> happily accepts and starts with values greater than the reported value.
> Really ?  If KVM is accepting a greater vCPU count than it reports
> via /dev/kvm, then we should fix the latter

Why?  We already allow oversubscription (you can run 3 guests with 1
vcpu each on a 2-cpu machine); we also allow pinning a 2-vcpu guest to 1
host cpu; so why can't we allow oversubscription from within a single
VM?  Sure, performance will be lousier, but that doesn't mean the
request is invalid.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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