Re: [PATCH v2 1/2 RESEND] sched/fair: take into account scheduling domain in select_idle_smt()

[Keisuke Nishimura]

> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 533547e3c90a..66457d4b8965 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -7311,13 +7311,19 @@ static int select_idle_core(struct task_struct *p, int core, struct cpumask *cpu
> >   /*
> >    * Scan the local SMT mask for idle CPUs.
> >    */
> > -static int select_idle_smt(struct task_struct *p, int target)
> > +static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int target)
> >   {
> >          int cpu;
> >
> >          for_each_cpu_and(cpu, cpu_smt_mask(target), p->cpus_ptr) {
> >                  if (cpu == target)
> >                          continue;
> > +               /*
> > +                * Check if the CPU is in the LLC scheduling domain of @target.
> > +                * Due to isolcpus, there is no guarantee that all the siblings are in the domain.
> > +                */
> > +               if (!cpumask_test_cpu(cpu, sched_domain_span(sd)))
>
> commit df3cb4ea1fb6 ("sched/fair: Fix wrong cpu selecting from isolated domain")
> also checked if (!cpumask_test_cpu(cpu, p->cpus_ptr) ||
>
> Why didn't you also re-add this test ?

Thank you for your comment. This is because the iterator "for_each_cpu_and(cpu, 
cpu_smt_mask(target), p->cpus_ptr)" ensures that cpu is included in p->cpus_ptr.

The iterator has changed. FYI, here is the change made in commit df3cb4ea1fb6:

        for_each_cpu(cpu, cpu_smt_mask(target)) {
-               if (!cpumask_test_cpu(cpu, p->cpus_ptr))
+               if (!cpumask_test_cpu(cpu, p->cpus_ptr) ||
+                   !cpumask_test_cpu(cpu, sched_domain_span(sd)))
                        continue;
                if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))

best,
Keisuke