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SubjectRe: 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@inria.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

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