linux-kernel - [RFC v2 4/9] sched/fair: Don't use CPU marked as avoid for wakeup and load balance

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Message-ID: <20250625191108.1646208-5-sshegde@linux.ibm.com>
Date: Thu, 26 Jun 2025 00:41:03 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, tglx@...utronix.de, yury.norov@...il.com,
        maddy@...ux.ibm.com
Cc: sshegde@...ux.ibm.com, vschneid@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, kprateek.nayak@....com, huschle@...ux.ibm.com,
        srikar@...ux.ibm.com, linux-kernel@...r.kernel.org,
        christophe.leroy@...roup.eu, linuxppc-dev@...ts.ozlabs.org,
        gregkh@...uxfoundation.org
Subject: [RFC v2 4/9] sched/fair: Don't use CPU marked as avoid for wakeup and load balance

Load balancer shouldn't spread CFS tasks into a CPU marked as Avoid. 
Remove those CPUs from load balancing decisions. 

At wakeup, don't select a CPU marked as avoid. 

Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
---
while tesing didn't see cpu being marked as avoid while new_cpu is. 
May need some more probing to see if even cpu can be. if so it could
lead to crash.  

 kernel/sched/fair.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7e2963efe800..406288aef535 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8546,7 +8546,12 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
 	}
 	rcu_read_unlock();
 
-	return new_cpu;
+	/* Don't select a CPU marked as avoid for wakeup */
+	if (cpu_avoid(new_cpu))
+		return cpu;
+	else
+		return new_cpu;
+
 }
 
 /*
@@ -11662,6 +11667,9 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq,
 
 	cpumask_and(cpus, sched_domain_span(sd), cpu_active_mask);
 
+	/* Don't spread load into CPUs marked as avoid */
+	cpumask_andnot(cpus, cpus, cpu_avoid_mask);
+
 	schedstat_inc(sd->lb_count[idle]);
 
 redo:
-- 
2.43.0