linux-kernel - Re: [PATCH v2 2/5] cpufreq/amd-pstate: add kernel command line to override dynamic epp

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Message-ID: <Z8q0DgATVY9YQ9Xe@BLRRASHENOY1.amd.com>
Date: Fri, 7 Mar 2025 14:23:34 +0530
From: "Gautham R. Shenoy" <gautham.shenoy@....com>
To: Mario Limonciello <superm1@...nel.org>
Cc: Perry Yuan <perry.yuan@....com>,
	Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>,
	"open list:CPU FREQUENCY SCALING FRAMEWORK" <linux-pm@...r.kernel.org>,
	Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v2 2/5] cpufreq/amd-pstate: add kernel command line to
 override dynamic epp

On Tue, Mar 04, 2025 at 09:23:24AM -0600, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@....com>
> 
> Add `amd_dynamic_epp=enable` and `amd_dynamic_epp=disable` to override
> the kernel configuration option `CONFIG_X86_AMD_PSTATE_DYNAMIC_EPP`
> locally.

Even with this patch, the user can switch the dynamic_epp value via
the sysfs file.  However, it is useful in case the
CONFIG_X86_AMD_PSTATE_DYNAMIC_EPP value is switched in the future.

I suspect that the servers will prefer to have this feature disabled
by default (they are always on AC power!) while the laptop/battery
operated devices would prefer to have this option enabled by default.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@....com>

-- 
Thanks and Regards
gautham.

> 
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  7 +++++++
>  Documentation/admin-guide/pm/amd-pstate.rst     |  7 +++++++
>  drivers/cpufreq/amd-pstate.c                    | 11 +++++++++++
>  3 files changed, 25 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index fb8752b42ec85..1afe6d8ab09bb 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -392,6 +392,13 @@
>  			disable
>  			  Disable amd-pstate preferred core.
>  
> +	amd_dynamic_epp=
> +			[X86]
> +			disable
> +			  Disable amd-pstate dynamic EPP.
> +			enable
> +			  Enable amd-pstate dynamic EPP.
> +
>  	amijoy.map=	[HW,JOY] Amiga joystick support
>  			Map of devices attached to JOY0DAT and JOY1DAT
>  			Format: <a>,<b>
> diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
> index 2e076650dc77c..8424e7119dd7e 100644
> --- a/Documentation/admin-guide/pm/amd-pstate.rst
> +++ b/Documentation/admin-guide/pm/amd-pstate.rst
> @@ -438,6 +438,13 @@ 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``.
>  
> +``amd_dynamic_epp``
> +
> +When AMD pstate is in auto mode, dynamic EPP will control whether the kernel
> +autonomously changes the EPP mode. The default is configured by
> +``CONFIG_X86_AMD_PSTATE_DYNAMIC_EPP`` but can be explicitly enabled with
> +``amd_pstate_epp=enable`` or disabled with ``amd_pstate_epp=disable``.
> +
>  User Space Interface in ``sysfs`` - General
>  ===========================================
>  
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index f00fb4ba9f26e..9911808fe0bcf 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1928,8 +1928,19 @@ static int __init amd_prefcore_param(char *str)
>  	return 0;
>  }
>  
> +static int __init amd_dynamic_epp_param(char *str)
> +{
> +	if (!strcmp(str, "disable"))
> +		dynamic_epp = false;
> +	if (!strcmp(str, "enable"))
> +		dynamic_epp = true;
> +
> +	return 0;
> +}
> +
>  early_param("amd_pstate", amd_pstate_param);
>  early_param("amd_prefcore", amd_prefcore_param);
> +early_param("amd_dynamic_epp", amd_dynamic_epp_param);
>  
>  MODULE_AUTHOR("Huang Rui <ray.huang@....com>");
>  MODULE_DESCRIPTION("AMD Processor P-state Frequency Driver");
> -- 
> 2.43.0
>