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The Intel P-state driver is currently undocumented. Add some documentation based on the cover-letter sent with the original series. Cc: Dirk Brandewie <dirk.brandewie@gmail.com> Acked-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
41 lines
1.6 KiB
Plaintext
41 lines
1.6 KiB
Plaintext
Intel P-state driver
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--------------------
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This driver implements a scaling driver with an internal governor for
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Intel Core processors. The driver follows the same model as the
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Transmeta scaling driver (longrun.c) and implements the setpolicy()
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instead of target(). Scaling drivers that implement setpolicy() are
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assumed to implement internal governors by the cpufreq core. All the
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logic for selecting the current P state is contained within the
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driver; no external governor is used by the cpufreq core.
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Intel SandyBridge+ processors are supported.
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New sysfs files for controlling P state selection have been added to
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/sys/devices/system/cpu/intel_pstate/
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max_perf_pct: limits the maximum P state that will be requested by
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the driver stated as a percentage of the available performance.
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min_perf_pct: limits the minimum P state that will be requested by
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the driver stated as a percentage of the available performance.
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no_turbo: limits the driver to selecting P states below the turbo
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frequency range.
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For contemporary Intel processors, the frequency is controlled by the
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processor itself and the P-states exposed to software are related to
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performance levels. The idea that frequency can be set to a single
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frequency is fiction for Intel Core processors. Even if the scaling
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driver selects a single P state the actual frequency the processor
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will run at is selected by the processor itself.
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New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
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deadband
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d_gain_pct
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i_gain_pct
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p_gain_pct
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sample_rate_ms
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setpoint
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