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Diffstat (limited to 'kernel/Documentation/cpu-freq/intel-pstate.txt')
| -rw-r--r-- | kernel/Documentation/cpu-freq/intel-pstate.txt | 64 |
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 |