path: root/Documentation/cpu-freq
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authorRamkumar Ramachandra <>2014-01-05 15:51:14 +0530
committerRafael J. Wysocki <>2014-01-06 01:14:25 +0100
commita3ea0153eca2a9de88fec1141426b589e8c8a2a1 (patch)
tree2627fa63428d4ca4d3c694e9eca4473e1e3c9f1c /Documentation/cpu-freq
parent72e2adcdcb0fa389ee78558b612c73f49641ed40 (diff)
Documentation / cpufreq: add intel-pstate.txt
The Intel P-state driver is currently undocumented. Add some documentation based on the cover-letter sent with the original series. Cc: Dirk Brandewie <> Acked-by: Randy Dunlap <> Signed-off-by: Ramkumar Ramachandra <> Signed-off-by: Rafael J. Wysocki <>
Diffstat (limited to 'Documentation/cpu-freq')
1 files changed, 40 insertions, 0 deletions
diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
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+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
+ max_perf_pct: limits the maximum P state that will be requested by
+ the driver stated as a percentage of the available performance.
+ min_perf_pct: limits the minimum P state that will be requested by
+ the driver stated as a percentage of the available performance.
+ 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