Messages in this thread | | | Date | Wed, 29 Dec 2021 10:13:04 +0100 (CET) | From | Julia Lawall <> | Subject | Re: cpufreq: intel_pstate: map utilization into the pstate range |
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On Tue, 28 Dec 2021, Rafael J. Wysocki wrote:
> 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.
The effect is the same. But that approach is indeed simpler than patching the kernel.
julia
> > > > > > > > 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 >
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