Re: [PATCH v3 06/10] sched/fair: Use the prefer_sibling flag of the current sched domain

[Ricardo Neri]

On Thu, Feb 16, 2023 at 01:16:42PM +0100, Peter Zijlstra wrote:
> On Wed, Feb 15, 2023 at 09:21:05PM -0800, Ricardo Neri wrote:
> 
> > I tweaked the solution that Dietmar proposed:
> > 
> > -	sds->prefer_sibling = child && child->flags & SD_PREFER_SIBLING;
> > +	if (sds->busiest)
> > +		sds->prefer_sibling = sds->busiest->flags & SD_PREFER_SIBLING;
> > 
> > This comes from the observation that the prefer_sibling setting acts on
> > busiest group. It then depends on whether the busiest group, not the local
> > group, has child sched sched domains. Today it works because in most cases
> > both the local and the busiest groups have child domains with the SD_
> > PREFER_SIBLING flag.
> > 
> > This would also satisfy sched domains with the SD_ASYM_CPUCAPACITY flag as
> > prefer_sibling would not be set in that case.
> > 
> > It would also conserve the current behavior at the NUMA level. We would
> > not need to implement SD_SPREAD_TASKS.
> > 
> > This would both fix the SMT vs non-SMT bug and be less invasive.
> > 
> > Thoughts?
> 
> That does look nice. Be sure to put in a nice comment too.

Will do!