linux-kernel - Re: [RFC PATCH v2 4/6] sched/fair: Introduce an energy estimation helper function

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Message-ID: <20180410125105.GC4043@hirez.programming.kicks-ass.net>
Date:   Tue, 10 Apr 2018 14:51:05 +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 4/6] sched/fair: Introduce an energy estimation
 helper function

On Fri, Apr 06, 2018 at 04:36:05PM +0100, Dietmar Eggemann wrote:
> +static inline
> +struct capacity_state *find_cap_state(int cpu, unsigned long util)
> +{
> +	struct sched_energy_model *em = *per_cpu_ptr(energy_model, cpu);
> +	struct capacity_state *cs = NULL;
> +	int i;
> +
> +	util += util >> 2;
> +
> +	for (i = 0; i < em->nr_cap_states; i++) {
> +		cs = &em->cap_states[i];
> +		if (cs->cap >= util)
> +			break;
> +	}
> +
> +	return cs;
> +}

So in the last thread there was some discussion about this; in
particular on how this related to schedutil and if we should tie it into
that.

I think for starters tying it to schedutil is not a bad idea; ideally
people _should_ migrate towards using that.

Also; I think it makes sense to better integrate cpufreq and the
energy-model values like what rjw already suggested, such that maybe we
can have cpufreq_driver_resolve_freq() return a structure containing the
relevant information for the selected frequency.

But implementing the frequency selection thing in multiple places like
now sounds like a very bad idea to me.