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Documentation: intel_pstate: Document HWP energy/performance hints 

Updated documentation for the support of energy performance hint in
the HWP mode.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
[ rjw: Subject & changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
hifive-unleashed-5.1
Srinivas Pandruvada 2016-12-06 13:32:17 -08:00 committed by Rafael J. Wysocki
parent 984edbdccc
commit bf006e149a
1 changed files with 24 additions and 0 deletions
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Documentation/cpu-freq/intel-pstate.txt
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@ -139,6 +139,30 @@ architecture of the processor permits:
- User can read write system wide turbo status
/sys/devices/system/cpu/no_turbo
Support of energy performance hints
It is possible to provide hints to the HWP algorithms in the processor
to be more performance centric to more energy centric. When the driver
is using HWP, two additional cpufreq sysfs attributes are presented for
each logical CPU.
These attributes are:
- energy_performance_available_preferences
- energy_performance_preference
To get list of supported hints:
$ cat energy_performance_available_preferences
default performance balance_performance balance_power power
The current preference can be read or changed via cpufreq sysfs
attribute "energy_performance_preference". Reading from this attribute
will display current effective setting. User can write any of the valid
preference string to this attribute. User can always restore to power-on
default by writing "default".
Since threads can migrate to different CPUs, this is possible that the
new CPU may have different energy performance preference than the previous
one. To avoid such issues, either threads can be pinned to specific CPUs
or set the same energy performance preference value to all CPUs.
Tuning Intel P-State driver
When the performance can be tuned using PID (Proportional Integral