1Intel P-state driver
   4This driver implements a scaling driver with an internal governor for
   5Intel Core processors.  The driver follows the same model as the
   6Transmeta scaling driver (longrun.c) and implements the setpolicy()
   7instead of target().  Scaling drivers that implement setpolicy() are
   8assumed to implement internal governors by the cpufreq core. All the
   9logic for selecting the current P state is contained within the
  10driver; no external governor is used by the cpufreq core.
  12Intel SandyBridge+ processors are supported.
  14New sysfs files for controlling P state selection have been added to
  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.
  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.
  23      no_turbo: limits the driver to selecting P states below the turbo
  24      frequency range.
  26For contemporary Intel processors, the frequency is controlled by the
  27processor itself and the P-states exposed to software are related to
  28performance levels.  The idea that frequency can be set to a single
  29frequency is fiction for Intel Core processors. Even if the scaling
  30driver selects a single P state the actual frequency the processor
  31will run at is selected by the processor itself.
  33New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
  35      deadband
  36      d_gain_pct
  37      i_gain_pct
  38      p_gain_pct
  39      sample_rate_ms
  40      setpoint
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