diff options
Diffstat (limited to 'Documentation/cpu-freq/intel-pstate.txt')
| -rw-r--r-- | Documentation/cpu-freq/intel-pstate.txt | 37 |
1 files changed, 25 insertions, 12 deletions
diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt index a69ffe1d54d5..765d7fc0e692 100644 --- a/Documentation/cpu-freq/intel-pstate.txt +++ b/Documentation/cpu-freq/intel-pstate.txt @@ -1,17 +1,28 @@ Intel P-state driver -------------------- -This 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. - -Intel SandyBridge+ processors are supported. - -New sysfs files for controlling P state selection have been added to +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 @@ -33,7 +44,9 @@ 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. -New debugfs files have also been added to /sys/kernel/debug/pstate_snb/ +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 |