[It's a good thing to keep the list Cc'd, someone else might have better answer] On Thu, Jan 12, 2017 at 10:33:23AM -0600, BharaniKumar Gedela wrote:

Hi Martin,

To be more clear on the requirement, I have a kind of VM which needs 2 vcpu's. One of the vcpu is dedicated for a specific process in the VM and the other vcpu can be shared by other VM's of the same kind. To be more clear, each VM is having 2 processes, one cpu intensive which got a dedicated vcpu alloted and the other process is a lightweight process which needs less amount of cpu so it can be shared with the other Vm's light weight processes. Example: There are 10 VM's of same type which need 2 vcpu's each (1 dedicated and 1 shared): VM#: vcpu1, vcpu2 VM1: 1, 11 VM2: 2, 11 VM3: 3, 11 VM4: 4, 11 VM5: 5, 11 VM6: 6, 11 VM7:7, 11 VM8: 8, 11 VM: 9, 11 VM:10, 11

OK, so this is easy to do in libvirt. You just use <vcpupin/>

IS there a way openstack nova-scheduler can provision the same (does this need libvirt changes if we want to provision via nova-scheduler)?or it can only be done via boot via xml (manually via templates in virsh)?

However, I don't know about openstack. But definitely there's no change needed in libvirt. There might be some people from openstack on this list, but it's mainly libvirt-related

Regards, Bharani..

On Thu, Jan 12, 2017 at 2:26 AM, Martin Kletzander <mkletzan@redhat.com> wrote:

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On Wed, Jan 11, 2017 at 11:13:52AM -0600, BharaniKumar Gedela wrote:

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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?

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

Regards,

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Bharani..

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