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Documentation / cpu-freq / intel-pstate.txt




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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:00 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.
19	
20	      min_perf_pct: limits the minimum P state that will be  requested by
21	      the driver stated as a percentage of the available performance.
22	
23	      no_turbo: limits the driver to selecting P states below the turbo
24	      frequency range.
25	
26	For contemporary Intel processors, the frequency is controlled by the
27	processor itself and the P-states exposed to software are related to
28	performance levels.  The idea that frequency can be set to a single
29	frequency is fiction for Intel Core processors. Even if the scaling
30	driver selects a single P state the actual frequency the processor
31	will run at is selected by the processor itself.
32	
33	New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
34	
35	      deadband
36	      d_gain_pct
37	      i_gain_pct
38	      p_gain_pct
39	      sample_rate_ms
40	      setpoint
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