linux-kernel - Re: [PATCH v4 9/9] Documentation: amd-pstate: add amd pstate driver mode introduction

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Date:   Mon, 14 Nov 2022 16:29:19 -0600
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Perry Yuan <Perry.Yuan@....com>, rafael.j.wysocki@...el.com,
        ray.huang@....com, viresh.kumar@...aro.org
Cc:     Deepak.Sharma@....com, Nathan.Fontenot@....com,
        Alexander.Deucher@....com, Shimmer.Huang@....com,
        Xiaojian.Du@....com, Li.Meng@....com, wyes.karny@....com,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 9/9] Documentation: amd-pstate: add amd pstate driver
 mode introduction

Please run this through a spell checker before v5.

On 11/10/2022 11:58, Perry Yuan wrote:
> Introduce ``amd-pstate`` CPPC has two operation modes:
> * CPPC Autonomous (active) mode
> * CPPC non-autonomous (passive) mode.
> active mode and passive mode can be choosed by whith different kernel parameters.

can be chosen by different kernel parameters

> 
> Signed-off-by: Perry Yuan <Perry.Yuan@....com>
> ---
>   Documentation/admin-guide/pm/amd-pstate.rst | 47 +++++++++++++++++++--
>   1 file changed, 43 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
> index e7488891b12f..6ba02a658b31 100644
> --- a/Documentation/admin-guide/pm/amd-pstate.rst
> +++ b/Documentation/admin-guide/pm/amd-pstate.rst
> @@ -302,11 +302,11 @@ efficiency frequency management method on AMD processors.
>   Kernel Module Options for ``amd-pstate``
>   =========================================
>   
> -.. _shared_mem:
> +.. legacy_cppc:
>   
> -``shared_mem``
> -Use a module param (shared_mem) to enable related processors manually with
> -**amd_pstate.shared_mem=1**.
> +``legacy_cppc``
> +Use a module param (legacy_cppc) to enable related processors manually with
> +**amd_pstate=legacy_cppc**.
>   Due to the performance issue on the processors with `Shared Memory Support
>   <perf_cap_>`_, we disable it presently and will re-enable this by default
>   once we address performance issue with this solution.
> @@ -321,6 +321,45 @@ If the CPU flags have ``cppc``, then this processor supports `Full MSR Support
>   <perf_cap_>`_. Otherwise, it supports `Shared Memory Support <perf_cap_>`_.
>   
>   
> +AMD Pstae Driver Operation Modes

Pstate

> +=================================
> +
> +``amd-pstate`` CPPC has two operation modes: CPPC Autonomous(active) mode and
> +CPPC non-autonomous(passive) mode.
> +active mode and passive mode can be choosed by whith different kernel parameters.

can be chosen by different kernel parameters

> +When in Autonomous mode, CPPC ignores requests done in the Desired Performance
> +Target register and takes into account only the values set to the Minimum requested
> +performance, Maximum requested performance, and Energy Performance Preference
> +registers. When Autonomous is disabled, it only considers the Desired Performance Target.
> +
> +Active Mode
> +------------
> +
> +``amd-pstate-epp``
> +
> +This is the low-level firmware control mode which is implemented by ``amd-pstate-epp``
> +driver with ``amd-pstate=active`` passed to the kernel in the command line.
> +In this mode, ``amd-pstate-epp`` driver provides a hint to the hardware if software
> +wants to bias toward performance (0x0) or energy efficiency (0xff) to the CPPC firmware.
> +then CPPC power algorithm will calculate the runtime workload and adjust the realtime
> +cores frequency according to the power supply and thermal, core voltage and some other
> +hardware conditions.
> +
> +Passive Mode
> +------------
> +
> +``amd-pstate``
> +
> +It will be enabled if the ``amd_pstate=passive`` is passed to the kernel in the command line.
> +In this mode, ``amd-pstate``driver software specifies a desired QoS target in the CPPC
> +performance scale as a relative number. This can be expressed as percentage of nominal
> +performance (infrastructure max). Below the nominal sustained performance level,
> +desired performance expresses the average performance level of the processor subject
> +to the Performance Reduction Tolerance register. Above the nominal performance level,
> +processor must provide at least nominal performance requested and go higher if current
> +operating conditions allow.
> +
> +
>   ``cpupower`` tool support for ``amd-pstate``
>   ===============================================
>