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authorSrinivas Pandruvada <srinivas.pandruvada@linux.intel.com>2016-12-07 00:32:17 +0300
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2016-12-08 03:43:05 +0300
commitbf006e149a5717a4614d44a62090ae98775af7a0 (patch)
treef3dd9733c2be117d9faef9be96444ba0c74989fd
parent984edbdccc6ff01b953492f72296685ce3ea2497 (diff)
downloadlinux-bf006e149a5717a4614d44a62090ae98775af7a0.tar.xz
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>
-rw-r--r--Documentation/cpu-freq/intel-pstate.txt24
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
index 198b2ef88aec..1953994ef5e6 100644
--- a/Documentation/cpu-freq/intel-pstate.txt
+++ b/Documentation/cpu-freq/intel-pstate.txt
@@ -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