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Date: Thu, 3 Mar 2016 19:26:24 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Linux PM list <linux-pm@...r.kernel.org>,
Juri Lelli <juri.lelli@....com>,
Steve Muckle <steve.muckle@...aro.org>,
ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
Viresh Kumar <viresh.kumar@...aro.org>,
Michael Turquette <mturquette@...libre.com>
Subject: Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler
utilization data
On Thu, Mar 03, 2016 at 05:28:55PM +0000, Dietmar Eggemann wrote:
> > +void arch_scale_freq_tick(void)
> > +{
> > + u64 aperf, mperf;
> > + u64 acnt, mcnt;
> > +
> > + if (!static_cpu_has(X86_FEATURE_APERFMPERF))
> > + return;
> > +
> > + aperf = rdmsrl(MSR_IA32_APERF);
> > + mperf = rdmsrl(MSR_IA32_APERF);
> > +
> > + acnt = aperf - this_cpu_read(arch_prev_aperf);
> > + mcnt = mperf - this_cpu_read(arch_prev_mperf);
> > +
> > + this_cpu_write(arch_prev_aperf, aperf);
> > + this_cpu_write(arch_prev_mperf, mperf);
> > +
> > + this_cpu_write(arch_cpu_freq, div64_u64(acnt * SCHED_CAPACITY_SCALE, mcnt));
>
> Wasn't there the problem that this ratio goes to zero if the cpu is idle
> in the old power estimation approach on x86?
Yeah, there was something funky.
SDM says they only count in C0 (ie. !idle), so it _should_ work.
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