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

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

On 5/20/2026 3:48 PM, Viresh Kumar wrote:
> On 11-05-26, 12:03, Zhongqiu Han wrote:
>> Just one small concern is that requested_freq may underflow as an
>> unsigned value; perhaps this could be improved by:
>>
>> -		if (requested_freq > freq_step)
>> +		if (requested_freq > policy->min + freq_step)
>>  			requested_freq -= freq_step;
>>  		else
>>  			requested_freq = policy->min;
> 
> Looks fine.
> 
>> or use min() func?
>>
>> Additionally, it seems that dropping the early‑exit checks also appears
>> to be a nice side effect fix for CPUFREQ_NEED_UPDATE_LIMITS drivers when
>> updating internal upper and lower frequency boundaries.
>>
>> As designed in commit 1c534352f47f ("cpufreq: Introduce
>> CPUFREQ_NEED_UPDATE_LIMITS driver flag"), a cpufreq driver may need to
>> update its internal frequency limits when policy min or max changes for
>> drivers setting CPUFREQ_NEED_UPDATE_LIMITS.
>>
>> However, the early‑exit in cs_dbs_update() can prevent
>> __cpufreq_driver_target() from ever being called.
>>
>> For example, when policy->min rises from 200 to 400 kHz while policy
>> ->cur is already at 400 kHz, under low load:
>>
>>   cpufreq_policy_apply_limits():
>>     policy->min(400) > policy->cur(400) ?  NO -> driver not called
>>
>>   cs_limits():
>>     dbs_info->requested_freq = policy->cur = 400
>>
>>   [next sampling period, low load]
>>   cs_dbs_update():
>>     requested_freq = 400
>>     if (requested_freq == policy->min)  /* 400 == 400 -> true */
>>         goto out;  /* __cpufreq_driver_target() never called */
>>
>> With the early‑exit removed, __cpufreq_driver_target() is called with
>> target == policy->cur, and CPUFREQ_NEED_UPDATE_LIMITS ensures the driver
>> is invoked to update its internal performance boundaries.
> 
> I think we are all in agreement on this now ?
> 

For CPUFREQ_NEED_UPDATE_LIMITS drivers, dropping this early-exit checks
means cpufreq_driver->target() will always be called every time when
cs_dbs_update() is called. Is it OK?