linux-kernel - Re: [tip:sched/core] sched/fair: Fix rounding bug for asym packing

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Date:   Mon, 21 Jan 2019 13:47:52 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        vincent.guittot@...aro.org, tglx@...utronix.de, hpa@...or.com,
        torvalds@...ux-foundation.org
Cc:     linux-tip-commits@...r.kernel.org, valentin.schneider@....com
Subject: Re: [tip:sched/core] sched/fair: Fix rounding bug for asym packing


Sorry guys, I seem to have messed this up :/

Valentin pointed me out that I missed v3 and v4 of these patches; v3 got
lost in the x-mas pile and v4 was actually on my todo list for this
week, but I'd forgotten I'd already queued v2.

I'll go queue delta patches.

On Mon, Jan 21, 2019 at 03:33:53AM -0800, tip-bot for Vincent Guittot wrote:
> index 50aa2aba69bd..2ccd6e093326 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8190,6 +8190,12 @@ static inline void update_sg_lb_stats(struct lb_env *env,
>  	/* Adjust by relative CPU capacity of the group */
>  	sgs->group_capacity = group->sgc->capacity;
>  	sgs->avg_load = (sgs->group_load*SCHED_CAPACITY_SCALE) / sgs->group_capacity;
> +	/*
> +	 * Prevent division rounding to make the computation of imbalance
> +	 * slightly less than original value and to prevent the rq to be then
> +	 * selected as busiest queue:
> +	 */
> +	sgs->avg_load += 1;
>  
>  	if (sgs->sum_nr_running)
>  		sgs->load_per_task = sgs->sum_weighted_load / sgs->sum_nr_running;