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

[Hongyan Xia]

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.

>   }
>   

Reviewed-by: Hongyan Xia <hongyan.xia@xxxxxxxxxxxxx>