CPU Overprovisioning

[Fariborz Navidan <md...@gmail.com>]

Hello,

How VMs receive CPU shares when cpu over provisioning factor is increased
and CPU cap is disabled for them?

Thanks

Re: CPU Overprovisioning

[Andrija Panic <an...@gmail.com>]

Assuming you are on KVM...total number of Shares = total number of Mhz
(cores * Mhz) / cpuOverprovisioningFactor - cpu shares get changed (after
changing cpu overprovisioning) only when you stop and start an existing VM.
So i.e. 2 vCPU of 2000 MHz VM, with CPU overprovisioning of 2 will get
(2*2000)/2= 2000 CPU shares

In that regards, there are no "reservation" specifically, but cpu shares
are "engaged" only when there is shortage of CPU cycles on the host,
otherwise is not applicable.

CPU cap has been implemented for KVM only in 4.12 (if not mistaken), but in
general even if CPU cap has been set on the offerings, if changing cpu
overprovisioning factor, cpu cap will NOT change on hypervisor side (can
confirm for XS and VMware but expect same for KVM in 4.12) - i.e. it always
stays the same.

Hope that helps,
Andrija

On Sun, Jul 7, 2019, 18:04 Fariborz Navidan <md...@gmail.com> wrote:

> Hello,
>
> How VMs receive CPU shares when cpu over provisioning factor is increased
> and CPU cap is disabled for them?
>
> Thanks
>