On Wed, 7 Apr 2021 at 11:55, Peter Zijlstra <pet...@infradead.org> wrote:
>
> On Wed, Apr 07, 2021 at 11:42:17AM +0200, Vincent Guittot wrote:
> > I would really prefer to keep that out of select_idle_cpu which aims to
> > merge in one
> > single loop the walk through sd_llc. In the case of select_idle_smt, this
> > is done outside
> > the loop:
>
> Fair enough.
>
> > @@ -6317,11 +6339,21 @@ static int select_idle_sibling(struct task_struct
> > *p, int prev, int target)
> > }
> > }
> >
> > + if (static_branch_likely(&sched_smt_present)) {
> > + smt = test_idle_cores(target, false);
> > + if (!smt && cpus_share_cache(prev, target)) {
> > + /* No idle core. Check if prev has an idle sibling. */
> > + i = select_idle_smt(p, sd, prev);
> > + if ((unsigned int)i < nr_cpumask_bits)
> > + return i;
> > + }
> > + }
> > +
> > sd = rcu_dereference(per_cpu(sd_llc, target));
> > if (!sd)
> > return target;
>
> It needs to be here, otherwise you're using @sd uninitialized.
argh yes...
>
> > - i = select_idle_cpu(p, sd, target);
> > + i = select_idle_cpu(p, sd, smt, target);
> > if ((unsigned)i < nr_cpumask_bits)
> > return i;
>
> Let me have another poke at it.
