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@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

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