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Rafael J. Wysocki authored
There may be reasons to use generic cpufreq governors (eg. schedutil) on Intel platforms instead of the intel_pstate driver's internal governor. However, that currently can only be done by disabling intel_pstate altogether and using the acpi-cpufreq driver instead of it, which is subject to limitations. First of all, acpi-cpufreq only works on systems where the _PSS object is present in the ACPI tables for all logical CPUs. Second, on those systems acpi-cpufreq will only use frequencies listed by _PSS which may be suboptimal. In particular, by convention, the whole turbo range is represented in _PSS as a single P-state and the frequency assigned to it is greater by 1 MHz than the greatest non-turbo frequency listed by _PSS. That may confuse governors to use turbo frequencies less frequently which may lead to suboptimal performance. For this reason, make it possible to use the intel_pstate driver with generic cpufreq governors as a "normal" cpufreq driver. That mode is enforced by adding intel_pstate=passive to the kernel command line and cannot be disabled at run time. In that mode, intel_pstate provides a cpufreq driver interface including the ->target() and ->fast_switch() callbacks and is listed in scaling_driver as "intel_cpufreq". Signed-off-by:
Rafael J. Wysocki <rafael.j.wysocki@intel.com> Tested-by:
Doug Smythies <dsmythies@telus.net>
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