Re: [PATCH 4/8] sched/fair: Use dst_cpu's capacity rather than group {min, max} capacity

[Qais Yousef <qais.yousef@arm.com>]

On 01/28/21 18:31, Valentin Schneider wrote:
> Comparing capacity extrema of local and source sched_group's doesn't make
> much sense when at the day of the day the imbalance will be pulled by a
> known env->dst_cpu, whose capacity can be anywhere within the local group's
> capacity extrema.
> 
> Replace group_smaller_{min, max}_cpu_capacity() with comparisons of the
> source group's min/max capacity and the destination CPU's capacity.
> 
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> ---

Reviewed-by: Qais Yousef <qais.yousef@arm.com>

Thanks

--
Qais Yousef

>  kernel/sched/fair.c | 31 +++----------------------------
>  1 file changed, 3 insertions(+), 28 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 58ce0b22fcb0..0959a770ecc0 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8352,26 +8352,6 @@ group_is_overloaded(unsigned int imbalance_pct, struct sg_lb_stats *sgs)
>  	return false;
>  }
>  
> -/*
> - * group_smaller_min_cpu_capacity: Returns true if sched_group sg has smaller
> - * per-CPU capacity than sched_group ref.
> - */
> -static inline bool
> -group_smaller_min_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
> -{
> -	return capacity_greater(ref->sgc->min_capacity, sg->sgc->min_capacity);
> -}
> -
> -/*
> - * group_smaller_max_cpu_capacity: Returns true if sched_group sg has smaller
> - * per-CPU capacity_orig than sched_group ref.
> - */
> -static inline bool
> -group_smaller_max_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
> -{
> -	return capacity_greater(ref->sgc->max_capacity, sg->sgc->max_capacity);
> -}
> -
>  static inline enum
>  group_type group_classify(unsigned int imbalance_pct,
>  			  struct sched_group *group,
> @@ -8523,15 +8503,10 @@ static bool update_sd_pick_busiest(struct lb_env *env,
>  	if (!sgs->sum_h_nr_running)
>  		return false;
>  
> -	/*
> -	 * Don't try to pull misfit tasks we can't help.
> -	 * We can use max_capacity here as reduction in capacity on some
> -	 * CPUs in the group should either be possible to resolve
> -	 * internally or be covered by avg_load imbalance (eventually).
> -	 */
> +	/* Don't try to pull misfit tasks we can't help */
>  	if (static_branch_unlikely(&sched_asym_cpucapacity) &&
>  	    sgs->group_type == group_misfit_task &&
> -	    (!group_smaller_max_cpu_capacity(sg, sds->local) ||
> +	    (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) ||
>  	     sds->local_stat.group_type != group_has_spare))
>  		return false;
>  
> @@ -8615,7 +8590,7 @@ static bool update_sd_pick_busiest(struct lb_env *env,
>  	 */
>  	if (sd_has_asym_cpucapacity(env->sd) &&
>  	    (sgs->group_type <= group_fully_busy) &&
> -	    (group_smaller_min_cpu_capacity(sds->local, sg)))
> +	    (capacity_greater(sg->sgc->min_capacity, capacity_of(env->dst_cpu))))
>  		return false;
>  
>  	return true;
> -- 
> 2.27.0
>