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

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Message-ID: <2bc9cf4e-9ef8-4ac9-b40f-4ac949494c86@kylinos.cn>
Date: Fri, 25 Jul 2025 08:32:50 +0800
From: Zihuan Zhang <zhangzihuan@...inos.cn>
To: "zhenglifeng (A)" <zhenglifeng1@...wei.com>,
 "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

Hi,

在 2025/7/24 19:28, zhenglifeng (A) 写道:
> 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.
>
Thank you for pointing it out, I will fix it in the next version.

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