Re: cputime takes cstate into consideration

[Ankur Arora]

On 7/9/19 5:38 AM, Peter Zijlstra wrote:
> On Mon, Jul 08, 2019 at 07:00:08PM -0700, Ankur Arora wrote:
> > On 2019-06-26 12:23 p.m., Thomas Gleixner wrote:
> > > On Wed, 26 Jun 2019, Raslan, KarimAllah wrote:
> > > > On Wed, 2019-06-26 at 10:54 -0400, Konrad Rzeszutek Wilk wrote:
> > > > > There were some ideas that Ankur (CC-ed) mentioned to me of using the perf
> > > > > counters (in the host) to sample the guest and construct a better
> > > > > accounting idea of what the guest does. That way the dashboard
> > > > > from the host would not show 100% CPU utilization.
> > > >
> > > > You can either use the UNHALTED cycles perf-counter or you can use MPERF/APERF
> > > > MSRs for that. (sorry I got distracted and forgot to send the patch)
> > >
> > > Sure, but then you conflict with the other people who fight tooth and nail
> > > over every single performance counter.
> > How about using Intel PT PwrEvt extensions? This should allow us to
> > precisely track idle residency via just MWAIT and TSC packets. Should
> > be pretty cheap too. It's post Cascade Lake though.
>
> That would fully claim PT just for this stupid accounting thing and be
> completely Intel specific.
>
> Just stop this madness already.
I see the point about just accruing guest time (in mwait or not) as
guest CPU time.
But, to take this madness a little further, I'm not sure I see why it
fully claims PT. AFAICS, we should be able to enable PwrEvt and whatever
else simultaneously.

Ankur

>