Re: [PATCH v4 1/6] sched/fair: Do not skip CPUs of similar capacity with busy SMT siblings

[Ricardo Neri]

On Mon, Jun 08, 2026 at 02:50:38PM +0100, Christian Loehle wrote:
> On 6/8/26 13:57, Ricardo Neri 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.
> > 
> > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
> 
> Nice find!
> Reviewed-by: Christian Loehle <christian.loehle@xxxxxxx>

Thanks! I will make more changes based on feedback from Chen Yu and
Prateek. You may want to reissue your tag after that :)