linux-kernel - Re: cpufreq: intel_pstate: map utilization into the pstate range

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Date:   Tue, 28 Dec 2021 18:46:25 +0100 (CET)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
cc:     Julia Lawall <julia.lawall@...ia.fr>,
        Francisco Jerez <currojerez@...eup.net>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: cpufreq: intel_pstate: map utilization into the pstate range



On Tue, 28 Dec 2021, Rafael J. Wysocki wrote:

> On Tue, Dec 28, 2021 at 5:58 PM Julia Lawall <julia.lawall@...ia.fr> wrote:
> >
> > I looked a bit more into why pstate 20 is always using the least energy. I
> > have just one thread spinning for 10 seconds, I use a fixed value for the
> > pstate, and I measure the energy usage with turbostat.
>
> How exactly do you fix the pstate?

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index e7af18857371..19440b15454c 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -400,7 +402,7 @@ static void sugov_update_single_perf(struct update_util_data *hook, u64 time,
 		sg_cpu->util = prev_util;

 	cpufreq_driver_adjust_perf(sg_cpu->cpu, map_util_perf(sg_cpu->bw_dl),
-				   map_util_perf(sg_cpu->util), sg_cpu->max);
+				   sysctl_sched_fixedfreq, sg_cpu->max);

 	sg_cpu->sg_policy->last_freq_update_time = time;
 }

------------------------------

sysctl_sched_fixedfreq is a variable that I added to sysfs.


>
> > I tried this on a
> > 2-socket Intel 6130 and a 4-socket Intel 6130.  The experiment runs 40
> > times.
> >
> > There seem to be only two levels of CPU energy usage.  On the 2-socket
> > machine the energy usage is around 600J up to pstate 20 and around 1000J
> > after that.  On the 4-socket machine it is twice that.
>
> These are the package power numbers from turbostat, aren't they?

Yes.

julia