linux-kernel - Re: [RFC PATCH v2 2/6] sched: Introduce energy models of CPUs

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Message-ID: <20180410115457.GB4043@hirez.programming.kicks-ass.net>
Date:   Tue, 10 Apr 2018 13:54:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     linux-kernel@...r.kernel.org,
        Quentin Perret <quentin.perret@....com>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        linux-pm@...r.kernel.org,
        Morten Rasmussen <morten.rasmussen@....com>,
        Chris Redpath <chris.redpath@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Valentin Schneider <valentin.schneider@....com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steve Muckle <smuckle@...gle.com>,
        Eduardo Valentin <edubezval@...il.com>
Subject: Re: [RFC PATCH v2 2/6] sched: Introduce energy models of CPUs

On Fri, Apr 06, 2018 at 04:36:03PM +0100, Dietmar Eggemann wrote:
> +		/*
> +		 * Build the energy model of one CPU, and link it to all CPUs
> +		 * in its frequency domain. This should be correct as long as
> +		 * they share the same micro-architecture.
> +		 */

Aside from the whole PM_OPP question; you should assert that assumption.
Put an explicit check for the uarch in and FAIL the init if that isn't
met.

I don't think it makes _ANY_ kind of sense to share a frequency domain
across uarchs and we should be very clear we're not going to support
anything like that.

I know DynamiQ strictly speaking allows that, but since it's insane, we
should consider that a bug in DynamiQ.