Re: [PATCH] cpufreq: conservative: Fix incorrect frequency decrease due to stale target

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

On 4/22/2026 4:06 PM, Stratos Karafotis wrote:
> Hi all!
> 
> I was struggling to see your point, but I think you are right.
> 
> The requested_freq could be equal to policy->min (due to idle periods)
> while the dbs_info->requested_freq could be greater than policy->min.
> So, in this case it breaks out early without the chance to further reduce the frequency, correct?

Yes. This is the case where problems arise.

> 
> Stratos Karafotis
> 
> On 4/21/26 15:35, Lifeng Zheng wrote:
>> In cs_dbs_update(), the requested frequency is decremented by one freq_step
>> for each idle period. However, this can cause divergence between
>> 'requested_freq' (target for current update) and 'dbs_info->requested_freq'
>> (target from previous update).
>>
>> When the load crosses up_threshold or down_threshold, the decision on
>> whether to increase or decrease frequency should be based on the *previous*
>> target (dbs_info->requested_freq), not the current one. Otherwise, the
>> update step may be skipped entirely if the current target has already hit a
>> boundary due to prior adjustments.
>>
>> Ensure that frequency scaling decisions are made using the correct
>> historical target, fixing cases where frequency fails to decrease despite
>> sustained idle periods.
>>
>> Fixes: 00bfe05889e9 ("cpufreq: conservative: Decrease frequency faster for deferred updates")
>> Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
>> ---
>>   drivers/cpufreq/cpufreq_conservative.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
>> index df01d33993d8..f3c3b54e4bf8 100644
>> --- a/drivers/cpufreq/cpufreq_conservative.c
>> +++ b/drivers/cpufreq/cpufreq_conservative.c
>> @@ -104,7 +104,7 @@ static unsigned int cs_dbs_update(struct cpufreq_policy *policy)
>>           dbs_info->down_skip = 0;
>>             /* if we are already at full speed then break out early */
>> -        if (requested_freq == policy->max)
>> +        if (dbs_info->requested_freq == policy->max)
>>               goto out;
>>             requested_freq += freq_step;
>> @@ -127,7 +127,7 @@ static unsigned int cs_dbs_update(struct cpufreq_policy *policy)
>>           /*
>>            * if we cannot reduce the frequency anymore, break out early
>>            */
>> -        if (requested_freq == policy->min)
>> +        if (dbs_info->requested_freq == policy->min)
>>               goto out;
>>             if (requested_freq > freq_step)
>