linux-kernel - Re: [PATCH] cpufreq/amd-pstate: Detect preferred core support before driver registration

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Message-ID: <9613611b-9417-4d96-912c-019220afc02f@amd.com>
Date: Mon, 9 Dec 2024 21:54:00 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: K Prateek Nayak <kprateek.nayak@....com>,
 "Gautham R. Shenoy" <gautham.shenoy@....com>, Huang Rui <ray.huang@....com>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Viresh Kumar <viresh.kumar@...aro.org>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Perry Yuan <perry.yuan@....com>,
 Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>
Subject: Re: [PATCH] cpufreq/amd-pstate: Detect preferred core support before
 driver registration

On 12/9/2024 21:25, K Prateek Nayak wrote:
> Booting with amd-pstate on 3rd Generation EPYC system incorrectly
> enabled ITMT support despite the system not supporting Preferred Core
> ranking. amd_pstate_init_prefcore() called during amd_pstate*_cpu_init()
> requires "amd_pstate_prefcore" to be set correctly however the preferred
> core support is detected only after driver registration which is too
> late.
> 
> Swap the function calls around to detect preferred core support before
> registring the driver via amd_pstate_register_driver(). This ensures
> amd_pstate*_cpu_init() sees the correct value of "amd_pstate_prefcore"
> considering the platform support.
> 
> Fixes: 279f838a61f9 ("x86/amd: Detect preferred cores in amd_get_boost_ratio_numerator()")
> Fixes: ff2653ded4d9 ("cpufreq/amd-pstate: Move registration after static function call update")
> Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>

Thanks for the fix.  I'll apply this to my fixes branch, do some further 
testing and will include this in a future 6.13-fixes PR.

Acked-by: Mario Limonciello <mario.limonciello@....com>

> ---
> This patch is based on the latest superm1/linux:bleeding-edge and was
> also tested on v6.13-rc2 upstream release. Following is the behavior on
> a 3rd Generation EPYC system with and without this fix:
> 
> o v6.13-rc2
> 
>      # cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
>      amd-pstate
> 
>      # cat /proc/sys/kernel/sched_itmt_enabled
>      1
> 
>      # echo Y > /sys/kernel/debug/sched/verbose
>      # cat /sys/kernel/debug/sched/domains/cpu0/domain*/flags
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY SD_SHARE_LLC SD_PREFER_SIBLING
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_LLC SD_ASYM_PACKING SD_PREFER_SIBLING
>      ...
> 
> o v6.13-rc2 + this patch
> 
>      # cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
>      amd-pstate
> 
>      # cat /proc/sys/kernel/sched_itmt_enabled
>      cat: /proc/sys/kernel/sched_itmt_enabled: No such file or directory
> 
>      root@...una:/home/amd# echo Y > /sys/kernel/debug/sched/verbose
>      root@...una:/home/amd# cat /sys/kernel/debug/sched/domains/cpu0/domain*/flags
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_CPUCAPACITY SD_SHARE_LLC SD_PREFER_SIBLING
>      SD_BALANCE_NEWIDLE SD_BALANCE_EXEC SD_BALANCE_FORK SD_WAKE_AFFINE SD_SHARE_LLC SD_PREFER_SIBLING
>      ...
> 
> System was booted with "amd_pstate=passive" cmdline.
> ---
>   drivers/cpufreq/amd-pstate.c | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index 66fb7aee95d2..cb03f7d6575c 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1862,18 +1862,18 @@ static int __init amd_pstate_init(void)
>   		static_call_update(amd_pstate_set_epp, shmem_set_epp);
>   	}
>   
> -	ret = amd_pstate_register_driver(cppc_state);
> -	if (ret) {
> -		pr_err("failed to register with return %d\n", ret);
> -		return ret;
> -	}
> -
>   	if (amd_pstate_prefcore) {
>   		ret = amd_detect_prefcore(&amd_pstate_prefcore);
>   		if (ret)
>   			return ret;
>   	}
>   
> +	ret = amd_pstate_register_driver(cppc_state);
> +	if (ret) {
> +		pr_err("failed to register with return %d\n", ret);
> +		return ret;
> +	}
> +
>   	dev_root = bus_get_dev_root(&cpu_subsys);
>   	if (dev_root) {
>   		ret = sysfs_create_group(&dev_root->kobj, &amd_pstate_global_attr_group);
> 
> base-commit: 1f2f221668b210107f1277901bb757f1d77de842