Messages in this thread Patch in this message | | | Date | Thu, 19 Dec 2019 11:02:32 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched, fair: Allow a small degree of load imbalance between SD_NUMA domains |
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On Wed, Dec 18, 2019 at 06:50:52PM +0000, Valentin Schneider wrote: > I'm quite sure you have reasons to have written it that way, but I was > hoping we could squash it down to something like: > --- > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 08a233e97a01..f05d09a8452e 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8680,16 +8680,27 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s > env->migration_type = migrate_task; > lsub_positive(&nr_diff, local->sum_nr_running); > env->imbalance = nr_diff >> 1; > - return; > + } else { > + > + /* > + * If there is no overload, we just want to even the number of > + * idle cpus. > + */ > + env->migration_type = migrate_task; > + env->imbalance = max_t(long, 0, (local->idle_cpus - > + busiest->idle_cpus) >> 1); > } > > /* > - * If there is no overload, we just want to even the number of > - * idle cpus. > + * Allow for a small imbalance between NUMA groups; don't do any > + * of it if there is at least half as many tasks / busy CPUs as > + * there are available CPUs in the busiest group > */ > - env->migration_type = migrate_task; > - env->imbalance = max_t(long, 0, (local->idle_cpus - > - busiest->idle_cpus) >> 1); > + if (env->sd->flags & SD_NUMA && > + (busiest->sum_nr_running < busiest->group_weight >> 1) && > + (env->imbalance < busiest->group_weight * (env->sd->imbalance_pct - 100) / 100))
Note that this form allows avoiding the division. Every time I see that /100 I'm thinking we should rename and make imbalance_pct a base-2 thing.
> + env->imbalance = 0; > + > return; > } >
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