Re: [PATCH 1/2] cpufreq: Fix re-boost issue after hotplugging a cpu

["zhenglifeng (A)" <zhenglifeng1@huawei.com>]

On 2025/1/15 20:50, Rafael J. Wysocki wrote:

> On Wed, Jan 15, 2025 at 12:18 PM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>>
>> On 15-01-25, 18:01, Lifeng Zheng wrote:
>>> It turns out that cpuX will stay on the base frequency after performing
>>> these operations:
>>>
>>> 1. boost all cpus: echo 1 > /sys/devices/system/cpu/cpufreq/boost
>>>
>>> 2. offline the cpu: echo 0 > /sys/devices/system/cpu/cpuX/online
>>>
>>> 3. deboost all cpus: echo 0 > /sys/devices/system/cpu/cpufreq/boost
>>>
>>> 4. online the cpu: echo 1 > /sys/devices/system/cpu/cpuX/online
>>>
>>> 5. boost all cpus again: echo 1 > /sys/devices/system/cpu/cpufreq/boost
>>>
>>> This is because max_freq_req of the policy is not updated during the
>>> online process, and the value of max_freq_req before the last offline is
>>> retained. When the CPU is boosted again, freq_qos_update_request() will
>>> do nothing because the old value is the same as the new one. This causes
>>> the CPU stay on the base frequency. Update max_freq_req (and
>>> min_freq_req of course) in cpufreq_online() will solve this problem.
>>>
>>> Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
>>> ---
>>>  drivers/cpufreq/cpufreq.c | 7 +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>>> index 1a4cae54a01b..03ae879d50b9 100644
>>> --- a/drivers/cpufreq/cpufreq.c
>>> +++ b/drivers/cpufreq/cpufreq.c
>>> @@ -1475,6 +1475,13 @@ static int cpufreq_online(unsigned int cpu)
>>>
>>>               blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
>>>                               CPUFREQ_CREATE_POLICY, policy);
>>> +     } else {
>>> +             ret = freq_qos_update_request(policy->min_freq_req, policy->min);
>>
>> This may not be required, as min-freq-req is never updated.
> 
> It gets updated via scaling_min_freq AFAICS.  Doesn't this matter?

If fact, scaling_min_freq cannot be operated when a cpu is offline. So this
update may indeed be unnecessary.

> 
>>> +             if (ret < 0)
>>> +                     goto out_destroy_policy;
>>> +             ret = freq_qos_update_request(policy->max_freq_req, policy->max);
>>> +             if (ret < 0)
>>> +                     goto out_destroy_policy;
>>>       }
>>>
>>>       if (cpufreq_driver->get && has_target()) {
>>> --