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-rw-r--r--Documentation/cpu-freq/intel-pstate.txt54
1 files changed, 49 insertions, 5 deletions
diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
index e6bd1e6512a5..1953994ef5e6 100644
--- a/Documentation/cpu-freq/intel-pstate.txt
+++ b/Documentation/cpu-freq/intel-pstate.txt
@@ -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
@@ -120,13 +120,57 @@ 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
+
+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 HWP mode is not used, debugfs files have also been added to allow the
-tuning of the internal governor algorithm. These files are located at
-/sys/kernel/debug/pstate_snb/. The algorithm uses a PID (Proportional
-Integral Derivative) controller. The PID tunable parameters are:
+When the performance can be tuned using PID (Proportional Integral
+Derivative) controller, debugfs files are provided for adjusting performance.
+They are presented under:
+/sys/kernel/debug/pstate_snb/
+The PID tunable parameters are:
deadband
d_gain_pct
i_gain_pct