[PATCH v2] cpufreq: schedutil: Skip busy-CPU hold when NOHZ is inactive

[PATCH v2] cpufreq: schedutil: Skip busy-CPU hold when NOHZ is inactive

[Avi Weiss]

sugov_hold_freq() uses the NOHZ idle-call counter to determine whether
a CPU has been idle recently. When NOHZ is disabled or fails to
activate, the counter does not advance, causing schedutil to treat
the CPU as continuously busy and potentially prevent frequency
reductions.

Skip the busy-CPU hold when tick_nohz_is_active() is false. This
also handles systems where NOHZ was enabled but never activated.

Fixes: b7eaf1aab9f8 ("cpufreq: schedutil: Avoid reducing frequency of busy CPUs prematurely")
Cc: stable@vger.kernel.org
Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
---
v2:
- use tick_nohz_is_active() instead of tick_nohz_enabled to also
  handle NOHZ enabled but never activated, as suggested by Zhan Xusheng

 kernel/sched/cpufreq_schedutil.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 14405a614991..50249cc1a594 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -397,6 +397,9 @@ static bool sugov_hold_freq(struct sugov_cpu *sg_cpu)
 	if (uclamp_rq_is_capped(cpu_rq(sg_cpu->cpu)))
 		return false;
 
+	if (!tick_nohz_is_active())
+		return false;
+
 	/*
 	 * Maintain the frequency if the CPU has not been idle recently, as
 	 * reduction is likely to be premature.

base-commit: fa4ad798f6f681031775266044ba1b0cf3c670bd
-- 
2.43.0