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

[Zhongqiu Han]

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;
 }
 
-- 
2.43.0