Re: [PATCH v5 1/6] sched/fair: Do not skip CPUs of similar capacity with busy SMT siblings

[Ricardo Neri]

On Tue, Jun 23, 2026 at 09:13:41AM +0200, Vincent Guittot wrote:
> On Tue, 23 Jun 2026 at 01:55, Ricardo Neri
> <ricardo.neri-calderon@xxxxxxxxxxxxxxx> wrote:
> >
> > When picking a busiest CPU with only one running task, the function
> > sched_balance_find_src_rq() skips candidate CPUs if the destination CPU has
> > less than ~5% extra capacity. This condition only holds if all the SMT
> > siblings of a CPU are idle.
> >
> > SMT siblings share the computing resources of a physical core and this
> > results in reduced capacity if more than one sibling is busy.
> >
> > Skipping a CPU as described would prevent the load balancer from pulling
> > tasks from a scheduling group previously and correctly identified as
> > group_smt_balance (i.e., one with more than one task running).
> >
> > Do not skip a candidate CPU of similar capacity if it has busy SMT
> > siblings.
> >
> > Reviewed-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> 
> Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

Thanks you!