Re: [PATCH 2/2] sched: use static_branch_likely() for the NUMA balancing tick check

[Gregory Price (Meta)]

On 2026-10-23 14:23 +0200, Vincent Guittot wrote:
> On Fri, 23 Oct 2026 at 04:31, Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> >
> > task_tick_fair() checks sched_numa_balancing on every tick. The
> > static_branch_unlikely() annotation reserves the nop for the disabled case,
> > so the default configuration (NUMA_BALANCING_DEFAULT_ENABLED=y) pays a
> > taken jump per tick. Flip the polarity to static_branch_likely() so that
> > the fast path matches the default.
> >
> > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> > Acked-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
> > ---
> >  kernel/sched/fair.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 973647ad6c2d..71dc47d6114d 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -15351,7 +15351,7 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
> >         if (queued)
> >                 return;
> >
> > -       if (static_branch_unlikely(&sched_numa_balancing))
> > +       if (static_branch_likely(&sched_numa_balancing))
> 
> static_branch_unlikely is used by default for other static keys too
> like  sched_cluster_active, sched_cache_active, __sched_core_enabled
> sched_asym_cpucapacity and others ...

every other instance checking sched_numa_balancing checks likely(), this
is the odd one out.

> So systems which don't enable them don't pay a jump when not using it.
> I don't see why numa should be different
> 

numa balancing ships enabled by default.

This just looks like cleanup to me.

-- 
~Gregory