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

On 6/26/25 05:32, Yury Norov wrote:

On Thu, Jun 26, 2025 at 12:41:03AM +0530, Shrikanth Hegde wrote:

quoted

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@linux.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;
+
  }

There are more 'return's in this function, but you patch only one...

I had seen it but forgot to add. (since eas wasn't enabled in the system so i forgot)

quoted

  
  /*

@@ -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