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

[Shrikanth Hegde]

On 6/26/25 05:32, Yury Norov wrote:
> On Thu, Jun 26, 2025 at 12:41:03AM +0530, Shrikanth Hegde wrote:
> > 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@xxxxxxxxxxxxx>
> > ---
> > 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)

> >   
> >   /*
> > @@ -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