linux-kernel - Re: [RFC PATCH v4 09/12] sched/fair: Introduce an energy estimation helper function

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Message-ID: <20180709152825.GA17598@e108498-lin.cambridge.arm.com>
Date:   Mon, 9 Jul 2018 16:28:26 +0100
From:   Quentin Perret <quentin.perret@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     rjw@...ysocki.net, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, gregkh@...uxfoundation.org,
        mingo@...hat.com, dietmar.eggemann@....com,
        morten.rasmussen@....com, chris.redpath@....com,
        patrick.bellasi@....com, valentin.schneider@....com,
        vincent.guittot@...aro.org, thara.gopinath@...aro.org,
        viresh.kumar@...aro.org, tkjos@...gle.com, joel@...lfernandes.org,
        smuckle@...gle.com, adharmap@...cinc.com, skannan@...cinc.com,
        pkondeti@...eaurora.org, juri.lelli@...hat.com,
        edubezval@...il.com, srinivas.pandruvada@...ux.intel.com,
        currojerez@...eup.net, javi.merino@...nel.org
Subject: Re: [RFC PATCH v4 09/12] sched/fair: Introduce an energy estimation
 helper function

On Monday 09 Jul 2018 at 14:01:38 (+0200), Peter Zijlstra wrote:
> On Fri, Jul 06, 2018 at 06:04:44PM +0100, Quentin Perret wrote:
> > 'max_util' is basically the util we use to request an OPP. 'sum_util' is
> > how long the CPUs will be running.
> 
> A indeed. But yes bit of a mess, but it wants doing I think.

OK, understood.

> Perhaps a little something like the below... The alternative is two
> separate but closely related functions, not sure which is better.
> 
> 
> enum schedutil_type {
> 	frequency_util,
> 	energy_util,
> };

Hmm, this should work ... Should we also try to avoid the code
duplication in scale_rt_capacity() ? This doesn't want dependencies on
schedutil I assume so a little bit of extra work is required.

What about moving schedutil_freq_util() to sched.h and give it a more
generic name (total_cpu_util() ?) with no dependencies on
CONFIG_CPU_FREQ_GOV_SCHEDUTIL ? Also, 'energy_util' would have to be
renamed I guess (busy_time_util ?).

Then scale_rt_capacity() can be turned into something like (totally
untested):

static unsigned long scale_rt_capacity(int cpu)
{
	unsigned long util = total_cpu_util(cpu, 0, busy_time_util);

	return arch_scale_cpu_capacity(NULL, cpu) - util;
}

Thoughts ?

Thanks,
Quentin