linux-kernel - Re: [PATCH 2/2] cpufreq: Specify default governor on command line

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Date:   Tue, 16 Jun 2020 10:01:43 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     rjw@...ysocki.net, rafael@...nel.org, arnd@...db.de,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        kernel-team@...roid.com, tkjos@...gle.com, adharmap@...eaurora.org
Subject: Re: [PATCH 2/2] cpufreq: Specify default governor on command line

On 15-06-20, 17:55, Quentin Perret wrote:
> +static void cpufreq_get_default_governor(void)
> +{
> +	default_governor = cpufreq_parse_governor(cpufreq_param_governor);
> +	if (!default_governor) {
> +		if (*cpufreq_param_governor)
> +			pr_warn("Failed to find %s\n", cpufreq_param_governor);
> +		default_governor = cpufreq_default_governor();

A module_get() never happened for this case and so maybe a
module_put() should never get called.

> +	}
> +}
> +
> +static void cpufreq_put_default_governor(void)
> +{
> +	if (!default_governor)
> +		return;
> +	module_put(default_governor->owner);
> +	default_governor = NULL;
> +}
> +
>  static int cpufreq_init_governor(struct cpufreq_policy *policy)
>  {
>  	int ret;
> @@ -2701,6 +2721,8 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
>  
>  	if (driver_data->setpolicy)
>  		driver_data->flags |= CPUFREQ_CONST_LOOPS;
> +	else
> +		cpufreq_get_default_governor();
>  
>  	if (cpufreq_boost_supported()) {
>  		ret = create_boost_sysfs_file();
> @@ -2769,6 +2791,7 @@ int cpufreq_unregister_driver(struct cpufreq_driver *driver)
>  	subsys_interface_unregister(&cpufreq_interface);
>  	remove_boost_sysfs_file();
>  	cpuhp_remove_state_nocalls_cpuslocked(hp_online);
> +	cpufreq_put_default_governor();
>  
>  	write_lock_irqsave(&cpufreq_driver_lock, flags);
>  
> @@ -2792,4 +2815,5 @@ static int __init cpufreq_core_init(void)
>  	return 0;
>  }

And since this is a per boot thing, there is perhaps no need of doing
these at driver register/unregister, I would rather do it at:
cpufreq_core_init() time itself and so we will never need to run
cpufreq_put_default_governor() and so can be removed.

And another thing I am not able to understand (despite you commenting
about that in the commit log) is what happens if the default governor
chosen is built as a module ?

-- 
viresh