linux-kernel - Re: [PATCH] sched/fair: Fix negative imbalance in imbalance calculation

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Message-ID: <20200326133055.GA5537@lorien.usersys.redhat.com>
Date:   Thu, 26 Mar 2020 09:30:55 -0400
From:   Phil Auld <pauld@...hat.com>
To:     Aubrey Li <aubrey.li@...el.com>
Cc:     vincent.guittot@...aro.org, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        linux-kernel@...r.kernel.org, tim.c.chen@...ux.intel.com,
        vpillai@...italocean.com, joel@...lfernandes.org,
        Aubrey Li <aubrey.li@...ux.intel.com>
Subject: Re: [PATCH] sched/fair: Fix negative imbalance in imbalance
 calculation

On Thu, Mar 26, 2020 at 01:42:29PM +0800 Aubrey Li wrote:
> A negative imbalance value was observed after imbalance calculation,
> this happens when the local sched group type is group_fully_busy,
> and the average load of local group is greater than the selected
> busiest group. Fix this problem by comparing the average load of the
> local and busiest group before imbalance calculation formula.
> 
> Suggested-by: Vincent Guittot <vincent.guittot@...aro.org>
> Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
> Cc: Phil Auld <pauld@...hat.com>
> ---
>  kernel/sched/fair.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c1217bf..4a2ba3f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8761,6 +8761,14 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
>  
>  		sds->avg_load = (sds->total_load * SCHED_CAPACITY_SCALE) /
>  				sds->total_capacity;
> +		/*
> +		 * If the local group is more loaded than the selected
> +		 * busiest group don't try to pull any tasks.
> +		 */
> +		if (local->avg_load >= busiest->avg_load) {
> +			env->imbalance = 0;
> +			return;
> +		}
>  	}
>  
>  	/*
> -- 
> 2.7.4
> 

I like this one better. Thanks!

Reviewed-by: Phil Auld <pauld@...hat.com>

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