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
+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``
===============================================
--
2.34.1
