On Tue, Aug 29, 2023 at 02:43:39PM +0800, Meng, Li (Jassmine) wrote: > Introduce AMD Pstate Preferred Core. > > check preferred core state: > $ cat /sys/devices/system/cpu/amd-pstate/prefcore > > Signed-off-by: Meng Li <li.meng@xxxxxxx> > --- > Documentation/admin-guide/pm/amd-pstate.rst | 54 +++++++++++++++++++++ > 1 file changed, 54 insertions(+) > > diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst > index 1cf40f69278c..400264d52007 100644 > --- a/Documentation/admin-guide/pm/amd-pstate.rst > +++ b/Documentation/admin-guide/pm/amd-pstate.rst > @@ -353,6 +353,48 @@ is activated. In this mode, driver requests minimum and maximum performance > level and the platform autonomously selects a performance level in this range > and appropriate to the current workload. > > +AMD Pstate Preferred Core > +================================= > + > +The core frequency is subjected to the process variation in semiconductors. > +Not all cores are able to reach the maximum frequency respecting the > +infrastructure limits. Consequently, AMD has redefined the concept of > +maximum frequency of a part. This means that a fraction of cores can reach > +maximum frequency. To find the best process scheduling policy for a given > +scenario, OS needs to know the core ordering informed by the platform through > +highest performance capability register of the CPPC interface. > + > +``AMD Pstate Preferred Core`` enables the scheduler to prefer scheduling on > +cores that can achieve a higher frequency with lower voltage. The preferred > +core rankings can dynamically change based on the workload, platform conditions, > +thermals and ageing. > + > +The priority metric will be initialized by the AMD Pstate driver. The AMD Pstate Please align with ``amd-pstate`` in the whole documentation. > +driver will also determine whether or not ``AMD Pstate Preferred Core`` is > +supported by the platform. > + > +AMD Pstate driver will provide an initial core ordering when the system boots. The same here. > +The platform uses the CPPC interfaces to communicate the core ranking to the > +operating system and scheduler to make sure that OS is choosing the cores > +with highest performance firstly for scheduling the process. When AMD Pstate > +driver receives a message with the highest performance change, it will > +update the core ranking and set the cpu's priority. > + > +AMD Preferred Core Switch > +================================= > +Kernel Parameters > +----------------- > + > +``AMD Pstate Preferred Core`` has two states: enable and disable. > +Enable/disable states can be chosen by different kernel parameters. > +Default enable ``AMD Pstate Preferred Core``. > + > +``amd_prefcore=disable`` > + > +for systems that support ``AMD Pstate Preferred Core``, the core rankings will > +always be advertised by the platform. But OS can choose to ignore that via the > +kernel parameter ``amd_prefcore=disable``. As the comment in previos patch, we would better to let developers know how to detect this function in the hardware. Thanks, Ray > + > User Space Interface in ``sysfs`` - General > =========================================== > > @@ -385,6 +427,18 @@ control its functionality at the system level. They are located in the > to the operation mode represented by that string - or to be > unregistered in the "disable" case. > > +``prefcore`` > + Preferred Core state of the driver: "enabled" or "disabled". > + > + "enabled" > + Enable the AMD Preferred Core. > + > + "disabled" > + Disable the AMD Preferred Core > + > + > + This attribute is read-only to check the state of Preferred Core. > + > ``cpupower`` tool support for ``amd-pstate`` > =============================================== > > -- > 2.34.1 >
