Re: [PATCH v5 1/6] cpufreq: Remove per-CPU QoS constraint

[Pierre Gondois <pierre.gondois@arm.com>]

On 3/13/26 09:57, Viresh Kumar wrote:
> On 25-02-26, 09:49, Pierre Gondois wrote:
>> policy->max_freq_req represents the maximum allowed frequency as
>> requested by the policyX/scaling_max_freq sysfs file. This request
>> applies to all CPUs of the policy. It is not possible to request
>> a per-CPU maximum frequency.
>>
>> Thus, the interaction between the policy boost and scaling_max_freq
>> settings should be handled by adding a boost specific QoS constraint.
>> This will be handled in the following patches.
>>
>> This patch reverts of:
>> commit 1608f0230510 ("cpufreq: Fix re-boost issue after hotplugging
>> a CPU")
>>
>> Reviewed-by: Lifeng Zheng <zhenglifeng1@huawei.com>
>> Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
>> ---
>>   drivers/cpufreq/cpufreq.c | 4 ----
>>   1 file changed, 4 deletions(-)
>>
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> index 4472bb1ec83c7..db414c052658b 100644
>> --- a/drivers/cpufreq/cpufreq.c
>> +++ b/drivers/cpufreq/cpufreq.c
>> @@ -1481,10 +1481,6 @@ static int cpufreq_policy_online(struct cpufreq_policy *policy,
>>   
>>   		blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
>>   				CPUFREQ_CREATE_POLICY, policy);
>> -	} else {
>> -		ret = freq_qos_update_request(policy->max_freq_req, policy->max);
>> -		if (ret < 0)
>> -			goto out_destroy_policy;
>>   	}
>>   
>>   	if (cpufreq_driver->get && has_target()) {
> Even if this change is required, I don't think this should be applied
> separately. Just reverting this will get the bug back, which was fixed by
> commit 1608f0230510. Individual patches shouldn't break kernel (and bisect) as
> much as possible.
>
I could not reproduce the original issue.

At the time of the patch and still now, calls to
freq_qos_update_request() are checked against negative values.
The only exception is when using the scaling_max_frequency sysfs
entry, but this is out of the scope.

So I don't see how:

commit 1608f0230510 ("cpufreq: Fix re-boost issue after hotplugging a CPU")

can prevent a CPU to reach the boost frequency.  The only path that
could fail and that I could reproduce was fixed by:

https://lore.kernel.org/all/852ff11c589e6300730d207baac195b2d9d8b95f.1745511526.git.viresh.kumar@linaro.org/

So the current conclusion is that "cpufreq: Fix re-boost issue after 
hotplugging a CPU"
was not the real fix