Re: [PATCH] sched/fair: Add SMT4 group_smt_balance handling

[Tim Chen]

On Tue, 2023-09-05 at 12:41 +0200, Peter Zijlstra wrote:
> On Thu, Jul 27, 2023 at 06:32:44AM -0700, Tim Chen wrote:
> 
> >  kernel/sched/fair.c | 18 ++++++++++++++++--
> >  1 file changed, 16 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index a87988327f88..566686c5f2bd 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -9563,7 +9563,7 @@ static inline long sibling_imbalance(struct lb_env *env,
> >  	imbalance /= ncores_local + ncores_busiest;
> >  
> >  	/* Take advantage of resource in an empty sched group */
> > -	if (imbalance == 0 && local->sum_nr_running == 0 &&
> > +	if (imbalance <= 1 && local->sum_nr_running == 0 &&
> >  	    busiest->sum_nr_running > 1)
> >  		imbalance = 2;
> >  
> > @@ -9751,6 +9751,20 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> >  		break;
> >  
> >  	case group_smt_balance:
> > +		/* no idle cpus on both groups handled by group_fully_busy below */
> > +		if (sgs->idle_cpus != 0 || busiest->idle_cpus != 0) {
> > +			if (sgs->idle_cpus > busiest->idle_cpus)
> > +				return false;
> > +			if (sgs->idle_cpus < busiest->idle_cpus)
> > +				return true;
> > +			if (sgs->sum_nr_running <= busiest->sum_nr_running)
> > +				return false;
> > +			else
> > +				return true;
> > +		}
> > +		goto fully_busy;
> > +		break;
> 
> This is really daft; why can't this simply be: fallthrough; ? At the
> very least that break must go.
> 
> 

Yes, the break should go.  I was adding the goto to prevent compiler
from complaining about fall through code.  The break no longer is needed.

Tim