Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 9e472f95 authored by Srinivas Pandruvada's avatar Srinivas Pandruvada Committed by Rafael J. Wysocki
Browse files

Documentation: intel_pstate: Update per core limits 



Document restriction on per core P-State control.

Signed-off-by: default avatarSrinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 5879f877

Documentation/cpu-freq/intel-pstate.txt

+20 −1
Original line number Diff line number Diff line
@@ -48,7 +48,7 @@ In addition to the frequency-controlling interfaces provided by the cpufreq 
core, the driver provides its own sysfs files to control the P-State selection.

These files have been added to /sys/devices/system/cpu/intel_pstate/.

Any changes made to these files are applicable to all CPUs (even in a

multi-package system).

multi-package system, Refer to later section on placing "Per-CPU limits").



      max_perf_pct: Limits the maximum P-State that will be requested by

      the driver. It states it as a percentage of the available performance. The
@@ -120,6 +120,25 @@ frequency is fictional for Intel Core processors. Even if the scaling 
driver selects a single P-State, the actual frequency the processor

will run at is selected by the processor itself.



Per-CPU limits



The kernel command line option "intel_pstate=per_cpu_perf_limits" forces

the intel_pstate driver to use per-CPU performance limits.  When it is set,

the sysfs control interface described above is subject to limitations.

- The following controls are not available for both read and write

	/sys/devices/system/cpu/intel_pstate/max_perf_pct

	/sys/devices/system/cpu/intel_pstate/min_perf_pct

- The following controls can be used to set performance limits, as far as the

architecture of the processor permits:

	/sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq

	/sys/devices/system/cpu/cpu*/cpufreq/scaling_min_freq

	/sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

- User can still observe turbo percent and number of P-States from

	/sys/devices/system/cpu/intel_pstate/turbo_pct

	/sys/devices/system/cpu/intel_pstate/num_pstates

- User can read write system wide turbo status

	/sys/devices/system/cpu/no_turbo



Tuning Intel P-State driver



When the performance can be tuned using PID (Proportional Integral