On Wed, 20 Jan 2021 at 10:12, Mel Gorman <mgor...@techsingularity.net> wrote:
>
> On Wed, Jan 20, 2021 at 02:00:18PM +0530, Gautham R Shenoy wrote:
> > > @@ -6157,18 +6169,31 @@ static int select_idle_cpu(struct task_struct *p,
> > > struct sched_domain *sd, int t
> > > }
> > >
> > > for_each_cpu_wrap(cpu, cpus, target) {
> > > - if (!--nr)
> > > - return -1;
> > > - if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
> > > - break;
> > > + if (smt) {
> > > + i = select_idle_core(p, cpu, cpus, &idle_cpu);
> > > + if ((unsigned int)i < nr_cpumask_bits)
> > > + return i;
> > > +
> > > + } else {
> > > + if (!--nr)
> > > + return -1;
> > > + i = __select_idle_cpu(cpu);
> > > + if ((unsigned int)i < nr_cpumask_bits) {
> > > + idle_cpu = i;
> > > + break;
> > > + }
> > > + }
> > > }
> > >
> > > - if (sched_feat(SIS_PROP)) {
> > > + if (smt)
> > > + set_idle_cores(this, false);
> >
> > Shouldn't we set_idle_cores(false) only if this was the last idle
> > core in the LLC ?
> >
>
> That would involve rechecking the cpumask bits that have not been
> scanned to see if any of them are an idle core. As the existance of idle
> cores can change very rapidly, it's not worth the cost.
But don't we reach this point only if we scanned all CPUs and didn't
find an idle core ?
If there is an idle core, it returns early
And in case of smt == true, nr is set to INt_MAX and we loop on all CPUs/cores
>
> --
> Mel Gorman
> SUSE Labs
