linux-kernel - Re: [PATCH RFC] sched/fair: Penalty the cfs task which executes mwait/hlt

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Message-ID: <ee2b6da2-be8c-2540-29e9-ffbb9fdfd3fc@redhat.com>
Date:   Mon, 13 Jan 2020 12:52:20 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Wanpeng Li <kernellwp@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        KarimAllah <karahmed@...zon.de>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Ankur Arora <ankur.a.arora@...cle.com>,
        christopher.s.hall@...el.com, hubert.chrzaniuk@...el.com,
        len.brown@...el.com, thomas.lendacky@....com, rjw@...ysocki.net
Subject: Re: [PATCH RFC] sched/fair: Penalty the cfs task which executes
 mwait/hlt

On 13/01/20 11:43, Peter Zijlstra wrote:
> So the very first thing we need to get sorted is that MPERF/TSC ratio
> thing. TurboStat does it, but has 'funny' hacks on like:
> 
>   b2b34dfe4d9a ("tools/power turbostat: KNL workaround for %Busy and Avg_MHz")
> 
> and I imagine that there's going to be more exceptions there. You're
> basically going to have to get both Intel and AMD to commit to this.
> 
> IFF we can get concensus on MPERF/TSC, then yes, that is a reasonable
> way to detect a VCPU being idle I suppose. I've added a bunch of people
> who seem to know about this.
> 
> Anyone, what will it take to get MPERF/TSC 'working' ?

Do we really need MPERF/TSC for this use case, or can we just track
APERF as well and do MPERF/APERF to compute the "non-idle" time?

Paolo