linux-kernel - Re: [PATCH v3 10/10] cpufreq: amd-pstate: automatically load pstate driver by default

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Date: Tue, 11 Jun 2024 14:35:23 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Perry Yuan <perry.yuan@....com>, gautham.shenoy@....com
Cc: rafael.j.wysocki@...el.com, viresh.kumar@...aro.org, Ray.Huang@....com,
 Borislav.Petkov@....com, Alexander.Deucher@....com, Xinmei.Huang@....com,
 Xiaojian.Du@....com, Li.Meng@....com, linux-pm@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 10/10] cpufreq: amd-pstate: automatically load pstate
 driver by default

On 6/11/2024 03:52, Perry Yuan wrote:
> If the `amd-pstate` driver is not loaded automatically by default,
> it is because the kernel command line parameter has not been added.
> To resolve this issue, it is necessary to call the `amd_pstate_set_driver()`
> function to enable the desired mode (passive/active/guided) before registering
> the driver instance.
> This ensures that the driver is loaded correctly without relying on the kernel
> command line parameter.
> 
> Meanwhle, user can add driver mode in command line which will override
> the kernel config default option.
> 
> [    0.917789] usb usb6: Manufacturer: Linux 6.9.0-rc6-amd-pstate-new-fix-v1 xhci-hcd
> [    0.982579] amd_pstate: failed to register with return -22

This is currently "intended" behavior.  There is a comment remaining in 
the driver at the moment not part of this patch:

/*
  * TODO: We need more time to fine tune processors with shared memory 
solution
  * with community together.
  *
  * There are some performance drops on the CPU benchmarks which reports 
from
  * Suse. We are co-working with them to fine tune the shared memory 
solution. So
  * we disable it by default to go acpi-cpufreq on these processors and 
add a
  * module parameter to be able to enable it manually for debugging.
  */

Would you say that the performance drops are worked out on the shared 
memory designs?

* If so; this comment should be dropped too in this patch.
* If not; this patch really shouldn't be done as is.

> 
> Reported-by: Andrei Amuraritei <andamu@...teo.net>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218705
> Signed-off-by: Perry Yuan <perry.yuan@....com>
> ---
>   drivers/cpufreq/amd-pstate.c | 27 ++++++++++++++++++---------
>   1 file changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index fa486dfaa7e8..6e5c398810bf 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1841,28 +1841,37 @@ static int __init amd_pstate_init(void)
>   	/* check if this machine need CPPC quirks */
>   	dmi_check_system(amd_pstate_quirks_table);
>   
> -	switch (cppc_state) {
> -	case AMD_PSTATE_UNDEFINED:
> +	/*
> +	 * get driver mode for loading from command line choice or kernel config
> +	 * cppc_state will be AMD_PSTATE_UNDEFINED if no command line input
> +	 * command line choice will override the kconfig option
> +	 */
> +	if (cppc_state == AMD_PSTATE_UNDEFINED) {
> +		pr_err("pyuan cppc_state == AMD_PSTATE_UNDEFINED \n");

Looks like a debug line escaped into the patch.

>   		/* Disable on the following configs by default:
>   		 * 1. Undefined platforms
>   		 * 2. Server platforms
>   		 * 3. Shared memory designs
>   		 */
>   		if (amd_pstate_acpi_pm_profile_undefined() ||
> -		    amd_pstate_acpi_pm_profile_server() ||
> -		    !cpu_feature_enabled(X86_FEATURE_CPPC)) {
> +		    amd_pstate_acpi_pm_profile_server()) {
>   			pr_info("driver load is disabled, boot with specific mode to enable this\n");
>   			return -ENODEV;
>   		}
> -		ret = amd_pstate_set_driver(CONFIG_X86_AMD_PSTATE_DEFAULT_MODE);
> -		if (ret)
> -			return ret;
> -		break;
> +		/* get driver mode from kernel config option [1:4] */
> +		cppc_state = CONFIG_X86_AMD_PSTATE_DEFAULT_MODE;
> +	}
> +
> +	switch (cppc_state) {
>   	case AMD_PSTATE_DISABLE:
> +		pr_info("driver load is disabled, boot with specific mode to enable this\n");
>   		return -ENODEV;
>   	case AMD_PSTATE_PASSIVE:
>   	case AMD_PSTATE_ACTIVE:
>   	case AMD_PSTATE_GUIDED:
> +		ret = amd_pstate_set_driver(cppc_state);
> +		if (ret)
> +			return ret;
>   		break;
>   	default:
>   		return -EINVAL;
> @@ -1883,7 +1892,7 @@ static int __init amd_pstate_init(void)
>   	/* enable amd pstate feature */
>   	ret = amd_pstate_enable(true);
>   	if (ret) {
> -		pr_err("failed to enable with return %d\n", ret);
> +		pr_err("failed to enable driver mode(%d)\n", cppc_state);
>   		return ret;
>   	}
>