Re: [RFC PATCH 7/9] sched: search SMT before LLC domain

[Subhra Mazumdar]

On 9/5/19 2:31 AM, Peter Zijlstra wrote:
> On Fri, Aug 30, 2019 at 10:49:42AM -0700, subhra mazumdar wrote:
> > Search SMT siblings before all CPUs in LLC domain for idle CPU. This helps
> > in L1 cache locality.
> > ---
> >   kernel/sched/fair.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 8856503..94dd4a32 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6274,11 +6274,11 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
> >   			return i;
> >   	}
> >   
> > -	i = select_idle_cpu(p, sd, target);
> > +	i = select_idle_smt(p, target);
> >   	if ((unsigned)i < nr_cpumask_bits)
> >   		return i;
> >   
> > -	i = select_idle_smt(p, target);
> > +	i = select_idle_cpu(p, sd, target);
> >   	if ((unsigned)i < nr_cpumask_bits)
> >   		return i;
> >   
> But it is absolutely conceptually wrong. An idle core is a much better
> target than an idle sibling.
This is select_idle_smt not select_idle_core.