Re: [PATCH 0/2] cpufreq: governor: Apply limits with target_freq instead of policy->cur

[zhenglifeng (A)]

On 3/5/2026 8:19 PM, Jie Zhan wrote:
> 
> On 2/10/2026 7:54 PM, Lifeng Zheng wrote:
>> The motivation for this patchset cames from a test on our platform:
>>
>> With conservative governor and some pressure on CPU, the frequency rapidly
>> reach the max supported frequency, such as 2GHz.
>>
>> Later, some frequency division strategies on our platform were triggered
>> and the actual frequency become 500MHz -- 1/4 of the OS distribution
>> frequency.
>>
>> At that time, if someone excecutes 'cat cpuinfo_cur_freq', the actual
>> frequency will become 250MHz -- 1/4 of the min supported frequency.
>>
>> After the platform recovering from the frequency division, the frequency
>> will stay on 1GHz, until the pressure disappear.
>>
>> The reason this happens is that in cpufreq_verify_current_freq(), if
>> policy->cur != new_freq, policy->update will be queued, which will
>> ultimately lead to a call to cpufreq_policy_apply_limits(), and update the
>> target frequency to policy->min. And then in cs_dbs_update(), since the
>> pressure never vanish, it will always hit the following branches:
>>
>> 	if (load > dbs_data->up_threshold) {
>> 		dbs_info->down_skip = 0;
>>
>> 		/* if we are already at full speed then break out early */
>> 		if (requested_freq == policy->max)
>> 			goto out;
>>
>> Therefore, the target frequency will always remain at the lowest frequency.
> I feel like this is a common issue that some special handling in the
> governor should happen when the frequency limits changes, i.e.
> governor->limits() gets called.  See 'limits_changed' or 'need_freq_update'
> in the schedutil governor.
> 
> Do you think it's reasonable to mark such a flag in 'cpufreq_policy' when
> its limits changes, and any governor can use that for their own code?

Yes. This is why I said 'The branching conditions in cs_dbs_update() may
not be strict enough'. However, using policy->cur to decide the target freq
is unreasonable to me. So this patch set is still meaningful I think.

> 
> Jie
>>
>> The branching conditions in cs_dbs_update() may not be strict enough, but
>> the root cause of this problem is that the target frequency was updated
>> when querying cpuinfo_cur_freq. For ondemand and schedutil governor,
>> although the frequency will not always remain at the lowest level without
>> rising, will still be min_freq in a short period of time when the query
>> action occurs.
>>
>> Using the freq requested by the governor to decide whether to update the
>> target frequency is more reasonable in cpufreq_policy_apply_limits().
>>
>> Lifeng Zheng (2):
>>   cpufreq: governor: Move requested_freq to policy_dbs_info
>>   cpufreq: governor: Apply limits with requested_freq or next_freq
>>
>>  drivers/cpufreq/cpufreq_conservative.c | 14 ++++----------
>>  drivers/cpufreq/cpufreq_governor.c     |  3 ++-
>>  drivers/cpufreq/cpufreq_governor.h     | 12 ++++++++++++
>>  drivers/cpufreq/cpufreq_ondemand.c     | 10 +++++-----
>>  include/linux/cpufreq.h                |  7 ++++---
>>  kernel/sched/cpufreq_schedutil.c       |  4 ++--
>>  6 files changed, 29 insertions(+), 21 deletions(-)
>>