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| author | Ramkumar Ramachandra <artagnon@gmail.com> | 2014-01-05 15:51:14 +0530 |
|---|---|---|
| committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2014-01-06 01:14:25 +0100 |
| commit | a3ea0153eca2a9de88fec1141426b589e8c8a2a1 (patch) | |
| tree | 2627fa63428d4ca4d3c694e9eca4473e1e3c9f1c /Documentation/cpu-freq | |
| parent | 72e2adcdcb0fa389ee78558b612c73f49641ed40 (diff) | |
| download | lwn-a3ea0153eca2a9de88fec1141426b589e8c8a2a1.tar.gz lwn-a3ea0153eca2a9de88fec1141426b589e8c8a2a1.zip | |
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 <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>
Diffstat (limited to 'Documentation/cpu-freq')
| -rw-r--r-- | Documentation/cpu-freq/intel-pstate.txt | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt new file mode 100644 index 000000000000..e742d21dbd96 --- /dev/null +++ b/Documentation/cpu-freq/intel-pstate.txt @@ -0,0 +1,40 @@ +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. + + 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 |