linux-kernel - Re: [RFCv7 PATCH 01/10] sched: Compute cpu capacity available at current frequency

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Message-ID: <20160226091446.GW6356@twins.programming.kicks-ass.net>
Date:	Fri, 26 Feb 2016 10:14:46 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Steve Muckle <steve.muckle@...aro.org>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Juri Lelli <Juri.Lelli@....com>,
	Patrick Bellasi <patrick.bellasi@....com>,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [RFCv7 PATCH 01/10] sched: Compute cpu capacity available at
 current frequency

On Fri, Feb 26, 2016 at 02:37:19AM +0100, Rafael J. Wysocki wrote:

> That's all correct, but my question should rather be: is arch the right
> granularity?
> 
> In theory, there may be ARM64-based platforms using ACPI and behaving
> like x86 in that respect in the future.

Ah, so I started these hooks way before the cpufreq/cpuidle etc.
integration push.

Maybe we should look at something like that, but performance is really
critical, you most definitely do not want 3 indirections just because
abstract framework crap, that's measurable overhead on these callsites.

Hence the current inline with constant value or single function call.
And if archs would want a selector, I would recommend boot time call
instruction rewrites a-la alternatives/paravirt.