[libvirt] Query regarding sharing of vcpu's (cpu alloc ratio 1.0) between VM's

[Martin Kletzander]

On Wed, Jan 11, 2017 at 11:13:52AM -0600, BharaniKumar Gedela wrote:
>HI,
>
>I have a Q about sharing a vcpu across Vm's (cpu alloc ratio 1.0 and HT not
>enabled)?
>
>I have a Use case where a VM needs vcpu's and one of the vcpu is dedicated
>to the VM for some traffic processing. We want the other vcpu which is used
>for control processing and can be shared with a similar VM's control
>processing.
>Is this possible and support in openstack/libvirt/KVM?
>

I can't wrap my head around it, but do you mean something like this:

| pCPUs         | 0 | 1 | 2 | 3 |
|---------------+---+---+---+---|
| VM #0's vCPUs | 0 | 1 | 2 |   |
| VM #1's vCPUs |   | 0 | 1 |   |

where VM #0 uses pCPU 0 exclusively and both VMs share pCPUs 1 and 2?

You can do that using vcpupin [1].  Do you want them to share the pCPUs
fairly?  You could theoretically utilize shares/period/quota for that,
making sure that the rest of the system is set up properly as well.

>If so could you please advice how to test it?
>


[1] https://libvirt.org/formatdomain.html#elementsCPUTuning

>Regards,
>Bharani..

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