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Date: Thu, 3 Mar 2016 17:42:05 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
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Subject: Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler
 utilization data
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On Thu, Mar 03, 2016 at 05:28:29PM +0100, Peter Zijlstra 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);

Actually reading MPERF increases the chances of this working.

> +
> +	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));
> +}