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Documentation: intel_pstate: Update per core limits

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Document restriction on per core P-State control.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Srinivas Pandruvada 2016-10-25 13:20:42 -07:00 committed by Rafael J. Wysocki
parent 5879f87739
commit 9e472f95e4
1 changed files with 20 additions and 1 deletions
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21
Documentation/cpu-freq/intel-pstate.txt
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@ -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