linux-kernel - Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler utilization data

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Date:	Thu, 3 Mar 2016 19:14:35 +0000
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Peter Zijlstra <peterz@...radead.org>
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 03/03/16 18:26, Peter Zijlstra wrote:
> 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.

I see, back than the problem was 0 capacity in idle but this is about
frequency.