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 [off-list ref]:

quoted

From: Rafael J. Wysocki <redacted>

The PID-base P-state selection algorithm used by intel_pstate for
Core processors is based on very weak foundations.  Namely, 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. 

Thanks,
Srinivas

Regards,
Wanpeng Li
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