summaryrefslogtreecommitdiffstats
path: root/kernel/Documentation/cpu-freq/intel-pstate.txt
diff options
context:
space:
mode:
Diffstat (limited to 'kernel/Documentation/cpu-freq/intel-pstate.txt')
-rw-r--r--kernel/Documentation/cpu-freq/intel-pstate.txt64
1 files changed, 64 insertions, 0 deletions
diff --git a/kernel/Documentation/cpu-freq/intel-pstate.txt b/kernel/Documentation/cpu-freq/intel-pstate.txt
new file mode 100644
index 000000000..655750743
--- /dev/null
+++ b/kernel/Documentation/cpu-freq/intel-pstate.txt
@@ -0,0 +1,64 @@
+Intel P-state driver
+--------------------
+
+This driver provides an interface to control the P state selection for
+SandyBridge+ Intel processors. The driver can operate two different
+modes based on the processor model legacy and Hardware P state (HWP)
+mode.
+
+In legacy mode the driver implements a scaling driver with an internal
+governor for Intel Core processors. The driver follows the same model
+as the Transmeta scaling driver (longrun.c) and implements the
+setpolicy() instead of target(). Scaling drivers that implement
+setpolicy() are assumed to implement internal governors by the cpufreq
+core. All the logic for selecting the current P state is contained
+within the driver; no external governor is used by the cpufreq core.
+
+In HWP mode P state selection is implemented in the processor
+itself. The driver provides the interfaces between the cpufreq core and
+the processor to control P state selection based on user preferences
+and reporting frequency to the cpufreq core. In this mode the
+internal governor code is disabled.
+
+In addtion to the interfaces provided by the cpufreq core for
+controlling frequency the driver provides sysfs files for
+controlling P state selection. These files have been added to
+/sys/devices/system/cpu/intel_pstate/
+
+ max_perf_pct: limits the maximum P state that will be requested by
+ the driver stated as a percentage of the available performance. The
+ available (P states) performance may be reduced by the no_turbo
+ setting described below.
+
+ min_perf_pct: limits the minimum P state that will be requested by
+ the driver stated as a percentage of the max (non-turbo)
+ performance level.
+
+ no_turbo: limits the driver to selecting P states below the turbo
+ frequency range.
+
+ turbo_pct: displays the percentage of the total performance that
+ is supported by hardware that is in the turbo range. This number
+ is independent of whether turbo has been disabled or not.
+
+ num_pstates: displays the number of pstates that are supported
+ by hardware. This number is independent of whether turbo has
+ been disabled or not.
+
+For contemporary Intel processors, the frequency is controlled by the
+processor itself and the P-states exposed to software are related to
+performance levels. The idea that frequency can be set to a single
+frequency is fiction 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.
+
+For legacy mode debugfs files have also been added to allow tuning of
+the internal governor algorythm. These files are located at
+/sys/kernel/debug/pstate_snb/ These files are NOT present in HWP mode.
+
+ deadband
+ d_gain_pct
+ i_gain_pct
+ p_gain_pct
+ sample_rate_ms
+ setpoint