Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1468263

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

Show all headers | View raw

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@rjwysocki.net>:
> > 
> > From: Rafael J. Wysocki <rafael.j.wysocki@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. 

Thanks,
Srinivas

> 
> Regards,
> Wanpeng Li
> --
> To unsubscribe from this list: send the line "unsubscribe linux-pm"
> in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: [RFC][PATCH 7/7] cpufreq: intel_pstate: Change P-state selection  algorithm for Core Wanpeng Li <kernellwp@gmail.com> - 2016-08-23 05:50 +0200
  Re: [RFC][PATCH 7/7] cpufreq: intel_pstate: Change P-state  selection algorithm for Core Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> - 2016-08-23 06:10 +0200
    Re: [RFC][PATCH 7/7] cpufreq: intel_pstate: Change P-state selection  algorithm for Core Wanpeng Li <kernellwp@gmail.com> - 2016-08-23 07:00 +0200
      Re: [RFC][PATCH 7/7] cpufreq: intel_pstate: Change P-state selection algorithm for Core "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-08-23 19:30 +0200

csiph-web