linux-kernel - [PATCH 3/5] sched/deadline: Fix accounting after global limits change

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Message-ID: <20250627115118.438797-4-juri.lelli@redhat.com>
Date: Fri, 27 Jun 2025 13:51:16 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Waiman Long <llong@...hat.com>
Cc: linux-kernel@...r.kernel.org,
	Marcel Ziswiler <marcel.ziswiler@...ethink.co.uk>,
	Luca Abeni <luca.abeni@...tannapisa.it>,
	Juri Lelli <juri.lelli@...hat.com>
Subject: [PATCH 3/5] sched/deadline: Fix accounting after global limits change

A global limits change (sched_rt_handler() logic) currently leaves stale
and/or incorrect values in variables related to accounting (e.g.
extra_bw).

Properly clean up per runqueue variables before implementing the change
and rebuild scheduling domains (so that accounting is also properly
restored) after such a change is complete.

Reported-by: Marcel Ziswiler <marcel.ziswiler@...ethink.co.uk>
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
---
 kernel/sched/deadline.c | 4 +++-
 kernel/sched/rt.c       | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 7a3b556d45a99..187f324565f92 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -3166,6 +3166,9 @@ void sched_dl_do_global(void)
 	if (global_rt_runtime() != RUNTIME_INF)
 		new_bw = to_ratio(global_rt_period(), global_rt_runtime());
 
+	for_each_possible_cpu(cpu)
+		init_dl_rq_bw_ratio(&cpu_rq(cpu)->dl);
+
 	for_each_possible_cpu(cpu) {
 		rcu_read_lock_sched();
 
@@ -3181,7 +3184,6 @@ void sched_dl_do_global(void)
 		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
 
 		rcu_read_unlock_sched();
-		init_dl_rq_bw_ratio(&cpu_rq(cpu)->dl);
 	}
 }
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 15d5855c542cb..be6e9bcbe82b6 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2886,6 +2886,12 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
 	sched_domains_mutex_unlock();
 	mutex_unlock(&mutex);
 
+	/*
+	 * After changing maximum available bandwidth for DEADLINE, we need to
+	 * recompute per root domain and per cpus variables accordingly.
+	 */
+	rebuild_sched_domains();
+
 	return ret;
 }
 
-- 
2.49.0