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

[Martin Kletzander]

[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 at redhat.com>
>wrote:
>
>> 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..
>>>
>>
>> --
>>> libvir-list mailing list
>>> libvir-list at redhat.com
>>> https://www.redhat.com/mailman/listinfo/libvir-list
>>>
>>
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