Re: [RFC][PATCH 7/7] cpufreq: intel_pstate: Change P-state selection algorithm for Core

[Srinivas Pandruvada]

On Tue, 2016-08-23 at 11:48 +0800, Wanpeng Li wrote:
> Hi Rafael,
> 2016-08-01 7:38 GMT+08:00 Rafael J. Wysocki <rjw@xxxxxxxxxxxxx>:
> > 
> > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > 
> > The PID-base P-state selection algorithm used by intel_pstate for
> > Core processors is based on very weak foundations.ÂÂNamely, its
> > decisions are mostly based on the values of the APERF and MPERF
> > feedback registers and it only estimates the actual utilization to
> > check if it is not extremely low (in order to avoid getting stuck
> > in the highest P-state in that case).
> > 
> > Since it generally causes the CPU P-state to ramp up quickly, it
> > leads to satisfactory performance, but the metric used by it is
> > only
> > really valid when the CPU changes P-states by itself (ie. in the
> > turbo
> > range) and if the P-state value set by the driver is treated by the
> > CPU as the upper limit on turbo P-states selected by it.
> 
> Do you mean CPU will ignore the request value which is submitted by
> intel_pstate driver in the turbo range, but respect the upper limit
> on
> the turbo P-states which is submitted by intel_pstate driver?
Any request to request a P-state even upper limit can be totally
ignored in turbo range.Â

Thanks,
Srinivas

> 
> Regards,
> Wanpeng Li
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