Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 28 Dec 2021 19:06:44 +0100 | Subject | Re: cpufreq: intel_pstate: map utilization into the pstate range |
| |
On Tue, Dec 28, 2021 at 6:46 PM Julia Lawall <julia.lawall@inria.fr> wrote: > > > > 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);
This is just changing the "target" hint given to the processor which may very well ignore it, though.
> > sg_cpu->sg_policy->last_freq_update_time = time; > } > > ------------------------------ > > sysctl_sched_fixedfreq is a variable that I added to sysfs.
If I were trying to fix a pstate, I would set scaling_max_freq and scaling_min_freq in sysfs for all CPUs to the same value.
That would cause intel_pstate to set HWP min and max to the same value which should really cause the pstate to be fixed, at least outside the turbo range of pstates.
> > > > > 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.
OK
| |