RE: [PATCH V11 6/7] Documentation: amd-pstate: introduce amd-pstate preferred core

[Yuan, Perry]

[AMD Official Use Only - General]

> -----Original Message-----
> From: Meng, Li (Jassmine) <Li.Meng@xxxxxxx>
> Sent: Wednesday, November 29, 2023 2:55 PM
> To: Rafael J . Wysocki <rafael.j.wysocki@xxxxxxxxx>; Huang, Ray
> <Ray.Huang@xxxxxxx>
> Cc: linux-pm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx;
> linux-acpi@xxxxxxxxxxxxxxx; Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>; linux-
> kselftest@xxxxxxxxxxxxxxx; Fontenot, Nathan <Nathan.Fontenot@xxxxxxx>;
> Sharma, Deepak <Deepak.Sharma@xxxxxxx>; Deucher, Alexander
> <Alexander.Deucher@xxxxxxx>; Limonciello, Mario
> <Mario.Limonciello@xxxxxxx>; Huang, Shimmer
> <Shimmer.Huang@xxxxxxx>; Yuan, Perry <Perry.Yuan@xxxxxxx>; Du,
> Xiaojian <Xiaojian.Du@xxxxxxx>; Viresh Kumar <viresh.kumar@xxxxxxxxxx>;
> Borislav Petkov <bp@xxxxxxxxx>; Oleksandr Natalenko
> <oleksandr@xxxxxxxxxxxxxx>; Meng, Li (Jassmine) <Li.Meng@xxxxxxx>;
> Karny, Wyes <Wyes.Karny@xxxxxxx>
> Subject: [PATCH V11 6/7] Documentation: amd-pstate: introduce amd-pstate
> preferred core
>
> 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@xxxxxxxxxxxxxx>
> Reviewed-by: Wyes Karny <wyes.karny@xxxxxxx>
> Reviewed-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> Reviewed-by: Huang Rui <ray.huang@xxxxxxx>
> Signed-off-by: Meng Li <li.meng@xxxxxxx>
> ---
>  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

Reviewed-by: Perry Yuan < perry.yuan@xxxxxxx>