Re: cputime takes cstate into consideration

From: Raslan, KarimAllah
Date: Wed Jun 26 2019 - 15:27:43 EST

On Wed, 2019-06-26 at 21:21 +0200, Peter Zijlstra wrote:
> On Wed, Jun 26, 2019 at 06:55:36PM +0000, Raslan, KarimAllah wrote:
> >
> > If the host is completely in no_full_hz mode and the pCPU is dedicated to aÂ
> > single vCPU/task (and the guest is 100% CPU bound and never exits), you wouldÂ
> > still be ticking in the host once every second for housekeeping, right? WouldÂ
> > not updating the mwait-time once a second be enough here?
> People are trying very hard to get rid of that remnant tick. Lets not
> add dependencies to it.
> IMO this is a really stupid issue, 100% time is correct if the guest
> does idle in pinned vcpu mode.

One use case for proper accounting (obviously for a slightly relaxed definitionÂ
or *proper*) is *external* monitoring of CPU utilization for scaling group
(i.e. more VMs will be launched when you reach a certain CPU utilization).
These external monitoring tools needs to account CPU utilization properly.

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