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Message-ID: <CAKfTPtBN3HpNMrztcmAwkGuW9uHaKBi9KoqdvBEHuxf7=078NA@mail.gmail.com>
Date: Wed, 7 Nov 2018 17:32:32 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Quentin Perret <quentin.perret@....com>
Cc: Peter Zijlstra <peterz@...radead.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
linux-kernel <linux-kernel@...r.kernel.org>,
"open list:THERMAL" <linux-pm@...r.kernel.org>,
"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
Ingo Molnar <mingo@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Morten Rasmussen <morten.rasmussen@....com>,
Chris Redpath <chris.redpath@....com>,
Patrick Bellasi <patrick.bellasi@....com>,
Valentin Schneider <valentin.schneider@....com>,
Thara Gopinath <thara.gopinath@...aro.org>,
viresh kumar <viresh.kumar@...aro.org>,
Todd Kjos <tkjos@...gle.com>,
Joel Fernandes <joel@...lfernandes.org>,
"Cc: Steve Muckle" <smuckle@...gle.com>, adharmap@...eaurora.org,
Saravana Kannan <skannan@...eaurora.org>,
pkondeti@...eaurora.org, Juri Lelli <juri.lelli@...hat.com>,
Eduardo Valentin <edubezval@...il.com>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
currojerez@...eup.net, Javi Merino <javi.merino@...nel.org>
Subject: Re: [PATCH v8 03/15] PM: Introduce an Energy Model management framework
Hi Quentin,
On Tue, 16 Oct 2018 at 12:15, Quentin Perret <quentin.perret@....com> wrote:
>
> +
> +/**
> + * em_pd_energy() - Estimates the energy consumed by the CPUs of a perf. domain
> + * @pd : performance domain for which energy has to be estimated
> + * @max_util : highest utilization among CPUs of the domain
> + * @sum_util : sum of the utilization of all CPUs in the domain
> + *
> + * Return: the sum of the energy consumed by the CPUs of the domain assuming
> + * a capacity state satisfying the max utilization of the domain.
> + */
> +static inline unsigned long em_pd_energy(struct em_perf_domain *pd,
> + unsigned long max_util, unsigned long sum_util)
> +{
> + unsigned long freq, scale_cpu;
> + struct em_cap_state *cs;
> + int i, cpu;
> +
> + /*
> + * In order to predict the capacity state, map the utilization of the
> + * most utilized CPU of the performance domain to a requested frequency,
> + * like schedutil.
> + */
> + cpu = cpumask_first(to_cpumask(pd->cpus));
> + scale_cpu = arch_scale_cpu_capacity(NULL, cpu);
> + cs = &pd->table[pd->nr_cap_states - 1];
> + freq = map_util_freq(max_util, cs->frequency, scale_cpu);
> +
> + /*
> + * Find the lowest capacity state of the Energy Model above the
> + * requested frequency.
> + */
> + for (i = 0; i < pd->nr_cap_states; i++) {
> + cs = &pd->table[i];
> + if (cs->frequency >= freq)
> + break;
> + }
> +
> + /*
> + * The capacity of a CPU in the domain at that capacity state (cs)
> + * can be computed as:
> + *
> + * cs->freq * scale_cpu
> + * cs->cap = -------------------- (1)
> + * cpu_max_freq
> + *
> + * So, ignoring the costs of idle states (which are not available in
> + * the EM), the energy consumed by this CPU at that capacity state is
> + * estimated as:
> + *
> + * cs->power * cpu_util
> + * cpu_nrg = -------------------- (2)
> + * cs->cap
> + *
> + * since 'cpu_util / cs->cap' represents its percentage of busy time.
> + *
> + * NOTE: Although the result of this computation actually is in
> + * units of power, it can be manipulated as an energy value
> + * over a scheduling period, since it is assumed to be
> + * constant during that interval.
> + *
> + * By injecting (1) in (2), 'cpu_nrg' can be re-expressed as a product
> + * of two terms:
> + *
> + * cs->power * cpu_max_freq cpu_util
> + * cpu_nrg = ------------------------ * --------- (3)
> + * cs->freq scale_cpu
> + *
> + * The first term is static, and is stored in the em_cap_state struct
> + * as 'cs->cost'.
> + *
> + * Since all CPUs of the domain have the same micro-architecture, they
> + * share the same 'cs->cost', and the same CPU capacity. Hence, the
> + * total energy of the domain (which is the simple sum of the energy of
> + * all of its CPUs) can be factorized as:
> + *
> + * cs->cost * \Sum cpu_util
> + * pd_nrg = ------------------------ (4)
> + * scale_cpu
> + */
> + return cs->cost * sum_util / scale_cpu;
Why do you need to keep scale_cpu outside the cs->cost ? do you expect
arch_scale_cpu_capacity() to change at runtime ?
If the returned value of arch_scale_cpu_capacity() changes, we will
have to rebuild several others things and we can include the update of
cs->cost
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