linux-kernel - Re: [PATCH v1] cpufreq: Avoid get

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Message-ID: <456c9900-1ce3-4a87-8c29-46e65e1240cb@huawei.com>
Date: Thu, 24 Jul 2025 19:28:21 +0800
From: "zhenglifeng (A)" <zhenglifeng1@...wei.com>
To: Zihuan Zhang <zhangzihuan@...inos.cn>, "rafael J . wysocki"
	<rafael@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>
CC: <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] cpufreq: Avoid get_governor() for first policy

On 2025/7/24 17:36, Zihuan Zhang wrote:

> When a cpufreq driver registers the first policy, it may attempt to
> initialize the policy governor from `last_governor`. However, this is
> meaningless for the first policy instance, because `last_governor` is
> only updated when policies are removed (e.g. during CPU offline).
> 
> The `last_governor` mechanism is intended to restore the previously
> used governor across CPU hotplug events. For the very first policy,
> there is no "previous governor" to restore, so calling
> get_governor(last_governor) is unnecessary and potentially confusing.
> 
> This patch skips looking up `last_governor` when registering the first
> policy. Instead, it directly uses the default governor after all
> governors have been registered and are available.
> 
> This avoids meaningless lookups, reduces unnecessary module reference
> handling, and simplifies the initial policy path.
> 
> Signed-off-by: Zihuan Zhang <zhangzihuan@...inos.cn>
> ---
>  drivers/cpufreq/cpufreq.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index d7426e1d8bdd..b5ebd4519eab 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1121,9 +1121,9 @@ static int cpufreq_init_policy(struct cpufreq_policy *policy)
>  	int ret;
>  
>  	if (has_target()) {
> -		/* Update policy governor to the one used before hotplug. */
> -		gov = get_governor(policy->last_governor);
> -		if (gov) {
> +		if (policy->last_governor[0] != '\0') {
> +			/* Update policy governor to the one used before hotplug. */
> +			gov = get_governor(policy->last_governor);

What if gov is null here? For example, the last governor has been removed.
The default governor should be used in this situation I think.

>  			pr_debug("Restoring governor %s for cpu %d\n",
>  				 gov->name, policy->cpu);
>  		} else {