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    Subject[PATCH V10 6/7] Documentation: amd-pstate: introduce amd-pstate preferred core
    Date
    Introduce amd-pstate preferred core.

    check preferred core state set by the kernel parameter:
    $ cat /sys/devices/system/cpu/amd-pstate/prefcore

    Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
    Reviewed-by: Wyes Karny <wyes.karny@amd.com>
    Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
    Reviewed-by: Huang Rui <ray.huang@amd.com>
    Signed-off-by: Meng Li <li.meng@amd.com>
    ---
    Documentation/admin-guide/pm/amd-pstate.rst | 59 ++++++++++++++++++++-
    1 file changed, 57 insertions(+), 2 deletions(-)

    diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
    index 1cf40f69278c..0b832ff529db 100644
    --- a/Documentation/admin-guide/pm/amd-pstate.rst
    +++ b/Documentation/admin-guide/pm/amd-pstate.rst
    @@ -300,8 +300,8 @@ platforms. The AMD P-States mechanism is the more performance and energy
    efficiency frequency management method on AMD processors.


    -AMD Pstate Driver Operation Modes
    -=================================
    +``amd-pstate`` Driver Operation Modes
    +======================================

    ``amd_pstate`` CPPC has 3 operation modes: autonomous (active) mode,
    non-autonomous (passive) mode and guided autonomous (guided) mode.
    @@ -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-pstate`` Preferred Core Switch
    +=================================
    +Kernel Parameters
    +-----------------
    +
    +``amd-pstate`` peferred 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 +427,19 @@ 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-pstate`` preferred core.
    +
    + "disabled"
    + Disable the ``amd-pstate`` preferred core
    +
    +
    + This attribute is read-only to check the state of preferred core set
    + by the kernel parameter.
    +
    ``cpupower`` tool support for ``amd-pstate``
    ===============================================

    --
    2.34.1
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