Introduce AMD Pstate Preferred Core.
check preferred core state: $ cat /sys/devices/system/cpu/amd-pstate/prefcore
Signed-off-by: Meng Li li.meng@amd.com --- 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 +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 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``. + 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`` ===============================================