linux-kernel - Re: [PATCH 2/2] cpufreq: Introduce a more generic way to set default per-policy boost flag

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Message-ID: <20250116065408.kjifylpgse5f3k3h@vireshk-i7>
Date: Thu, 16 Jan 2025 12:24:08 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Lifeng Zheng <zhenglifeng1@...wei.com>
Cc: rafael@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linuxarm@...wei.com,
	jonathan.cameron@...wei.com, zhanjie9@...ilicon.com,
	lihuisong@...wei.com, fanghao11@...wei.com
Subject: Re: [PATCH 2/2] cpufreq: Introduce a more generic way to set default
 per-policy boost flag

On 15-01-25, 18:01, Lifeng Zheng wrote:
> In cpufreq_online() of cpufreq.c, the per-policy boost flag is already set
> to mirror the cpufreq_driver boost during init but using freq_table to
> judge if the policy has boost frequency. There are two drawbacks to this
> approach:
> 
> 1. It doesn't work for the cpufreq drivers that do not use a frequency
> table. For now, acpi-cpufreq and amd-pstate have to enable boost in policy
> initialization. And cppc_cpufreq never set policy to boost when going
> online no matter what the cpufreq_driver boost flag is.
> 
> 2. If the cpu goes offline when cpufreq_driver boost enabled and then goes
> online when cpufreq_driver boost disabled, the per-policy boost flag will
> unreasonably remain true.

Yeah, this is a problem. I agree. If the global boost is disabled,
then boost shouldn't be allowed for any of the policies.

> Running set_boost at the end of the online process is a more generic way
> for all cpufreq drivers.
> 
> Signed-off-by: Lifeng Zheng <zhenglifeng1@...wei.com>
> ---
>  drivers/cpufreq/cpufreq.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 03ae879d50b9..867bda3decfd 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1409,10 +1409,6 @@ static int cpufreq_online(unsigned int cpu)
>  			goto out_free_policy;
>  		}
>  
> -		/* Let the per-policy boost flag mirror the cpufreq_driver boost during init */
> -		if (cpufreq_boost_enabled() && policy_has_boost_freq(policy))
> -			policy->boost_enabled = true;
> -
>  		/*
>  		 * The initialization has succeeded and the policy is online.
>  		 * If there is a problem with its frequency table, take it
> @@ -1576,6 +1572,18 @@ static int cpufreq_online(unsigned int cpu)
>  	if (new_policy && cpufreq_thermal_control_enabled(cpufreq_driver))
>  		policy->cdev = of_cpufreq_cooling_register(policy);
>  
> +	/* Let the per-policy boost flag mirror the cpufreq_driver boost during init */
> +	if (cpufreq_boost_supported()) {
> +		policy->boost_enabled = cpufreq_boost_enabled();
> +		ret = cpufreq_driver->set_boost(policy, policy->boost_enabled);

Maybe we can optimize here and not call set_boost() if policy's
boost_enabled is not changing at all.
        if (policy->boost_enabled != cpufreq_boost_enabled()) {
                policy->boost_enabled = cpufreq_boost_enabled();
                ret = cpufreq_driver->set_boost(policy, policy->boost_enabled);
                ...
        }

After this patch, maybe you should simplify the drivers as well, which
take care of enabling/boost at boot time or setting this flag ?

> +		if (ret) {
> +			/* If the set_boost fails, the online operation is not affected */
> +			pr_info("%s: CPU%d: Cannot %s BOOST\n", __func__, policy->cpu,
> +				policy->boost_enabled ? "enable" : "disable");
> +			policy->boost_enabled = !policy->boost_enabled;
> +		}
> +	}
> +
>  	pr_debug("initialization complete\n");
>  
>  	return 0;

-- 
viresh