2016-08-23 12:08 GMT+08:00 Srinivas Pandruvada <srinivas.pandruv...@linux.intel.com>: > 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 <r...@rjwysocki.net>: >> > >> > From: Rafael J. Wysocki <rafael.j.wyso...@intel.com> >> > >> > 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.
How to understand Rafael's description "if the P-state value set by the driver is treated by the CPU as the upper limit on the turbo P-states selected by it"? The upper limit will be totally ignored in turbo range. Regards, Wanpeng Li
