linux-kernel - [PATCH v2] sched: cpuset: Don't rebuild sched domains on suspend-resume

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Date:   Fri, 20 Jan 2023 19:48:22 +0000
From:   Qais Yousef <qyousef@...alina.io>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Waiman Long <longman@...hat.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>, tj@...nel.org,
        linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        cgroups@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Wei Wang <wvw@...gle.com>, Rick Yiu <rickyiu@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Qais Yousef <qyousef@...alina.io>
Subject: [PATCH v2] sched: cpuset: Don't rebuild sched domains on suspend-resume

Commit f9a25f776d78 ("cpusets: Rebuild root domain deadline accounting information")
enabled rebuilding sched domain on cpuset and hotplug operations to
correct deadline accounting.

Rebuilding sched domain is a slow operation and we see 10+ ms delay on
suspend-resume because of that.

Since nothing is expected to change on suspend-resume operation; skip
rebuilding the sched domains to regain the time lost.

Debugged-by: Rick Yiu <rickyiu@...gle.com>
Signed-off-by: Qais Yousef (Google) <qyousef@...alina.io>
---

    Changes in v2:
    
    	* Remove redundant check in update_tasks_root_domain() (Thanks Waiman)
    
    v1 link:
    
    	https://lore.kernel.org/lkml/20221216233501.gh6m75e7s66dmjgo@airbuntu/

 kernel/cgroup/cpuset.c  | 3 +++
 kernel/sched/deadline.c | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index a29c0b13706b..9a45f083459c 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1088,6 +1088,9 @@ static void rebuild_root_domains(void)
 	lockdep_assert_cpus_held();
 	lockdep_assert_held(&sched_domains_mutex);
 
+	if (cpuhp_tasks_frozen)
+		return;
+
 	rcu_read_lock();
 
 	/*
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0d97d54276cc..42c1143a3956 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2575,6 +2575,9 @@ void dl_clear_root_domain(struct root_domain *rd)
 {
 	unsigned long flags;
 
+	if (cpuhp_tasks_frozen)
+		return;
+
 	raw_spin_lock_irqsave(&rd->dl_bw.lock, flags);
 	rd->dl_bw.total_bw = 0;
 	raw_spin_unlock_irqrestore(&rd->dl_bw.lock, flags);
-- 
2.25.1