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Message-ID: <20231009062310.5zjzg4avv36o4vvg@BLR-5CG13462PL.amd.com>
Date: Mon, 9 Oct 2023 11:53:48 +0530
From: Wyes Karny <wyes.karny@....com>
To: Meng Li <li.meng@....com>
CC: Wyes Karny <wyes.karny@....com>,
"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
Huang Rui <ray.huang@....com>, <linux-pm@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <x86@...nel.org>,
<linux-acpi@...r.kernel.org>,
Shuah Khan <skhan@...uxfoundation.org>,
<linux-kselftest@...r.kernel.org>,
Nathan Fontenot <nathan.fontenot@....com>,
Deepak Sharma <deepak.sharma@....com>,
Alex Deucher <alexander.deucher@....com>,
Mario Limonciello <mario.limonciello@....com>,
Shimmer Huang <shimmer.huang@....com>,
Perry Yuan <Perry.Yuan@....com>,
Xiaojian Du <Xiaojian.Du@....com>,
Viresh Kumar <viresh.kumar@...aro.org>,
Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH V8 6/7] Documentation: amd-pstate: introduce amd-pstate preferred core
On 09 Oct 10:49, Meng Li wrote:
> Introduce amd-pstate preferred core.
>
> check preferred core state set by the kernel parameter:
> $ cat /sys/devices/system/cpu/amd-pstate/prefcore
>
> Reviewed-by: Mario Limonciello <mario.limonciello@....com>
> Reviewed-by: Huang Rui <ray.huang@....com>
Reviewed-by: Wyes Karny <wyes.karny@....com>
> Signed-off-by: Meng Li <li.meng@....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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