On Tue, 2016-11-01 at 14:11 -0700, Doug Smythies wrote: > On 2016.10.22 17:17 Rafael J. Wysocki wrote: > > > > > From: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > > > > 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". > > It is not clear to me why users that currently use > intel_pstate=disable on the kernel command line would benefit from > this change. Two reasons I think: - We have a big turbo zone, where current acpi-cpufreq can't select any target frequency even if controllable.
- We can still target ACPI-CPPC compatible devices in legacy mode and later in non-legacy mode. Thanks, Srinivas
