On 8/8/2023 03:10, Meng Li wrote:

Introduce AMD Pstate Preferred Core.

check preferred core state: $ cat /sys/devices/system/cpu/amd-pstate/prefcore_state

Signed-off-by: Meng Li li.meng@amd.com

Documentation/admin-guide/pm/amd-pstate.rst | 55 +++++++++++++++++++++ 1 file changed, 55 insertions(+)

diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst index 1cf40f69278c..4a30cf235425 100644 --- a/Documentation/admin-guide/pm/amd-pstate.rst +++ b/Documentation/admin-guide/pm/amd-pstate.rst @@ -353,6 +353,49 @@ 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`` use ITMT arch provides functions and data structures +for enabling the scheduler to favor scheduling on cores can be get a higher frequency +with lower voltage under preferred core.

This sentence was useful for the commit message, but I don't think it should be in the user facing documentation.

And it has the ability to dynamically +change the preferred core based on the workload and platform conditions and +accounting for thermals and aging.

+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 disable ``AMD Pstate Preferred Core``.

Why default disable?

+``amd_prefcore=enable``

+If ``amd_prefcore=enable`` is passed to kernel command line option +then enable ``AMD Pstate Preferred Core`` if the processor and power +firmware can support preferred core feature.

This can be simplified as "platform can support the preferred core feature".

• User Space Interface in ``sysfs`` - General

@@ -385,6 +428,18 @@ 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_state``

• 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.
  

As the attribute is read only and won't change at runtime, I don't think it makes sense to include the word "state" in the sysfs file name.

You can just rename it to "prefcore".

• ``cpupower`` tool support for ``amd-pstate``