Based on kernel version 3.19. Page generated on 2015-02-13 21:16 EST.
1 Intel P-state driver 2 -------------------- 3 4 This driver provides an interface to control the P state selection for 5 SandyBridge+ Intel processors. The driver can operate two different 6 modes based on the processor model legacy and Hardware P state (HWP) 7 mode. 8 9 In legacy mode the driver implements a scaling driver with an internal 10 governor for Intel Core processors. The driver follows the same model 11 as the Transmeta scaling driver (longrun.c) and implements the 12 setpolicy() instead of target(). Scaling drivers that implement 13 setpolicy() are assumed to implement internal governors by the cpufreq 14 core. All the logic for selecting the current P state is contained 15 within the driver; no external governor is used by the cpufreq core. 16 17 In HWP mode P state selection is implemented in the processor 18 itself. The driver provides the interfaces between the cpufreq core and 19 the processor to control P state selection based on user preferences 20 and reporting frequency to the cpufreq core. In this mode the 21 internal governor code is disabled. 22 23 In addtion to the interfaces provided by the cpufreq core for 24 controlling frequency the driver provides sysfs files for 25 controlling P state selection. These files have been added to 26 /sys/devices/system/cpu/intel_pstate/ 27 28 max_perf_pct: limits the maximum P state that will be requested by 29 the driver stated as a percentage of the available performance. The 30 available (P states) performance may be reduced by the no_turbo 31 setting described below. 32 33 min_perf_pct: limits the minimum P state that will be requested by 34 the driver stated as a percentage of the max (non-turbo) 35 performance level. 36 37 no_turbo: limits the driver to selecting P states below the turbo 38 frequency range. 39 40 For contemporary Intel processors, the frequency is controlled by the 41 processor itself and the P-states exposed to software are related to 42 performance levels. The idea that frequency can be set to a single 43 frequency is fiction for Intel Core processors. Even if the scaling 44 driver selects a single P state the actual frequency the processor 45 will run at is selected by the processor itself. 46 47 For legacy mode debugfs files have also been added to allow tuning of 48 the internal governor algorythm. These files are located at 49 /sys/kernel/debug/pstate_snb/ These files are NOT present in HWP mode. 50 51 deadband 52 d_gain_pct 53 i_gain_pct 54 p_gain_pct 55 sample_rate_ms 56 setpoint