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

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Message-ID: <20200113122911.GE2827@hirez.programming.kicks-ass.net>
Date:   Mon, 13 Jan 2020 13:29:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Wanpeng Li <kernellwp@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        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
Subject: Re: [PATCH RFC] sched/fair: Penalty the cfs task which executes
 mwait/hlt

On Mon, Jan 13, 2020 at 12:18:46PM +0100, Rafael J. Wysocki wrote:
> On Monday, January 13, 2020 11:43:14 AM CET Peter Zijlstra wrote:

> > Anyone, what will it take to get MPERF/TSC 'working' ?
> 
> The same thing that intel_pstate does.

But intel_pstate cheats, it has a FMS listing and possible 'interesting'
chips are excluded. For instance, Core2 has APERF/MPERF, but
intel_pstate does not support Core2.

Simlarly, intel_pstate does (obviously) not support AMD chips, even tho
those have APERF/MPERF.

Although I suppose Core2 doesn't have VMX and is therefore less
interesting, but then we'd need to gate the logic with something like:

	static_cpu_has(X86_FEATURE_APERFMPERF) &&
	(static_cpu_has(X86_FEATURE_VMX) || static_cpu_has(X86_FEATURE_SVM)

> Generally speaking, it shifts the mperf values by a number of positions
> depending on the CPU model, but that is 1 except for KNL.
> 
> See get_target_pstate().

I'm going to go out on a limb and guess that's the same KNL hack as
TurboStat has.

Is that really the only known case?