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: <17c7ed77-21f1-4093-91fc-f3eaa863d312@huawei.com>
Date: Thu, 16 Jan 2025 16:30:36 +0800
From: "zhenglifeng (A)" <zhenglifeng1@...wei.com>
To: Viresh Kumar <viresh.kumar@...aro.org>
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 2025/1/16 14:54, Viresh Kumar wrote:

> 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);
>                 ...
>         }

Makes sense. Thanks.

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

OK. I'll try to.

> 
>> +		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;
>