linux-kernel - Re: cputime takes cstate into consideration

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Message-ID: <7f721d94-aa19-20a4-6930-9ed4d1cd4834@oracle.com>
Date:   Mon, 8 Jul 2019 19:00:08 -0700
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        "Raslan, KarimAllah" <karahmed@...zon.de>
Cc:     "boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
        "joao.m.martins@...cle.com" <joao.m.martins@...cle.com>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "kernellwp@...il.com" <kernellwp@...il.com>,
        "mtosatti@...hat.com" <mtosatti@...hat.com>
Subject: Re: cputime takes cstate into consideration

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.

Ankur

> 
> Thanks,
> 
> 	tglx
>