[deliverable/linux.git] / Documentation / cpu-freq / intel-pstate.txt

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
/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.

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.

New debugfs files have also been added to /sys/kernel/debug/pstate_snb/

      deadband
      d_gain_pct
      i_gain_pct
      p_gain_pct
      sample_rate_ms
      setpoint
Commit	Line	Data
a3ea0153 RR	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
41629a82 DB	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.
a3ea0153 RR	21
a3ea0153 RR	22	min_perf_pct: limits the minimum P state that will be requested by
41629a82 DB	23	the driver stated as a percentage of the max (non-turbo)
41629a82 DB	24	performance level.
a3ea0153 RR	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