linux-kernel - [PATCH 6/7] sched/fair: Remove on_null

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Date: Wed,  3 Apr 2024 17:05:38 +0200
From: Pierre Gondois <pierre.gondois@....com>
To: linux-kernel@...r.kernel.org
Cc: Aaron Lu <aaron.lu@...el.com>,
	Rui Zhang <rui.zhang@...el.com>,
	Pierre Gondois <pierre.gondois@....com>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	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>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Waiman Long <longman@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.com>
Subject: [PATCH 6/7] sched/fair: Remove on_null_domain() and redundant checks

CPUs with a NULL sched domain are removed from the HKR_TYPE_SCHED
isolation mask. The two following checks are equialent:
- !housekeeping_runtime_test_cpu(cpu, HKR_TYPE_SCHED)
- on_null_domain(rq)

Remove on_null_domain() and the redundant checks.

Signed-off-by: Pierre Gondois <pierre.gondois@....com>
---
 kernel/sched/fair.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3e0f2a0f153f..9657c8f2176b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11830,11 +11830,6 @@ static void sched_balance_domains(struct rq *rq, enum cpu_idle_type idle)
 
 }
 
-static inline int on_null_domain(struct rq *rq)
-{
-	return unlikely(!rcu_dereference_sched(rq->sd));
-}
-
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * NOHZ idle load balancing (ILB) details:
@@ -12040,7 +12035,7 @@ void nohz_balance_exit_idle(struct rq *rq)
 	SCHED_WARN_ON(rq != this_rq());
 
 	/* If we're a completely isolated CPU, we don't play: */
-	if (on_null_domain(rq))
+	if (!housekeeping_runtime_test_cpu(cpu_of(rq), HKR_TYPE_SCHED))
 		return;
 
 	if (likely(!rq->nohz_tick_stopped))
@@ -12090,12 +12085,8 @@ void nohz_balance_enter_idle(int cpu)
 	 */
 	rq->has_blocked_load = 1;
 
-	/* Spare idle load balancing on CPUs that don't want to be disturbed: */
-	if (!housekeeping_runtime_test_cpu(cpu, HKR_TYPE_SCHED))
-		return;
-
 	/* If we're a completely isolated CPU, we don't play: */
-	if (on_null_domain(rq))
+	if (!housekeeping_runtime_test_cpu(cpu, HKR_TYPE_SCHED))
 		return;
 
 	/*
@@ -12504,11 +12495,14 @@ static __latent_entropy void sched_balance_softirq(struct softirq_action *h)
  */
 void sched_balance_trigger(struct rq *rq)
 {
+	int cpu = cpu_of(rq);
+
 	/*
 	 * Don't need to rebalance while attached to NULL domain or
 	 * runqueue CPU is not active
 	 */
-	if (unlikely(on_null_domain(rq) || !cpu_active(cpu_of(rq))))
+	if (unlikely(!housekeeping_runtime_test_cpu(cpu, HKR_TYPE_SCHED)) ||
+	    !cpu_active(cpu))
 		return;
 
 	if (time_after_eq(jiffies, rq->next_balance))
-- 
2.25.1