Re: [PATCH] cpufreq: schedutil: Fix uncleared need_freq_update on the adjust_perf path

[Christian Loehle]

On 6/17/26 05:06, Hongyan Xia wrote:
> On 6/16/2026 11:47 PM, Zhongqiu Han wrote:
>> The need_freq_update flag makes sugov_should_update_freq() return true
>> regardless of the rate_limit_us throttling, and is cleared in
>> sugov_update_next_freq(). sugov_update_single_freq() and
>> sugov_update_shared() go through that helper, so the flag does not
>> persist there.
>>
>> However, sugov_update_single_perf() (used by drivers implementing the
>> ->adjust_perf() callback, e.g. intel_pstate or amd-pstate in passive mode)
>> calls cpufreq_driver_adjust_perf() directly and never goes through
>> sugov_update_next_freq(), so the need_freq_update flag is not cleared in
>> that path.
>>
>> Before commit 75da043d8f88 ("cpufreq/sched: Set need_freq_update in
>> ignore_dl_rate_limit()"), this was effectively harmless because
>> sugov_should_update_freq() still honoured the rate limit even when
>> need_freq_update was set. After that change, the flag forces
>> sugov_should_update_freq() to always return true, so once set, it stays
>> effective indefinitely on the adjust_perf path.
>>
>> As a result, cpufreq_driver_adjust_perf() gets called on every scheduler
>> utilization update (with the runqueue lock held) rather than being
>> throttled by rate_limit_us, even if the driver itself may skip redundant
>> hardware updates.
>>
>> Clear need_freq_update at the end of the adjust_perf path as well.
>>
>> Fixes: 75da043d8f88 ("cpufreq/sched: Set need_freq_update in ignore_dl_rate_limit()")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Zhongqiu Han <zhongqiu.han@xxxxxxxxxxxxxxxx>
>> ---
>>   kernel/sched/cpufreq_schedutil.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
>> index ae9fd211cec1..a4e689eefdfb 100644
>> --- a/kernel/sched/cpufreq_schedutil.c
>> +++ b/kernel/sched/cpufreq_schedutil.c
>> @@ -486,6 +486,7 @@ static void sugov_update_single_perf(struct update_util_data *hook, u64 time,
>>   	cpufreq_driver_adjust_perf(sg_policy->policy, sg_cpu->bw_min,
>>   				   sg_cpu->util, max_cap);
>>   
>> +	sg_policy->need_freq_update = false;
>>   	sg_policy->last_freq_update_time = time;
> 
> Nice catch. Thanks.
> 
> It does seem to me that setting last_freq_update_time should then assert 
> !need_freq_update, otherwise it doesn't make sense, but that's a 
> different topic.
+1, feel free to submit that too.

For $SUBJECT:
Reviewed-by: Christian Loehle <christian.loehle@xxxxxxx>