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Documentation / cpu-freq / intel-pstate.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:36 EST.

1	Intel P-state driver
2	--------------------
3	
4	This driver implements a scaling driver with an internal governor for
5	Intel Core processors.  The driver follows the same model as the
6	Transmeta scaling driver (longrun.c) and implements the setpolicy()
7	instead of target().  Scaling drivers that implement setpolicy() are
8	assumed to implement internal governors by the cpufreq core. All the
9	logic for selecting the current P state is contained within the
10	driver; no external governor is used by the cpufreq core.
11	
12	Intel SandyBridge+ processors are supported.
13	
14	New sysfs files for controlling P state selection have been added to
15	/sys/devices/system/cpu/intel_pstate/
16	
17	      max_perf_pct: limits the maximum P state that will be requested by
18	      the driver stated as a percentage of the available performance. The
19	      available (P states) performance may be reduced by the no_turbo
20	      setting described below.
21	
22	      min_perf_pct: limits the minimum P state that will be  requested by
23	      the driver stated as a percentage of the max (non-turbo)
24	      performance level.
25	
26	      no_turbo: limits the driver to selecting P states below the turbo
27	      frequency range.
28	
29	For contemporary Intel processors, the frequency is controlled by the
30	processor itself and the P-states exposed to software are related to
31	performance levels.  The idea that frequency can be set to a single
32	frequency is fiction for Intel Core processors. Even if the scaling
33	driver selects a single P state the actual frequency the processor
34	will run at is selected by the processor itself.
35	
36	New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
37	
38	      deadband
39	      d_gain_pct
40	      i_gain_pct
41	      p_gain_pct
42	      sample_rate_ms
43	      setpoint
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