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Subject: Re: [PATCH v3 04/10] sched/fair: rework load_balance
To:     Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Phil Auld <pauld@redhat.com>,
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        Quentin Perret <quentin.perret@arm.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Morten Rasmussen <Morten.Rasmussen@arm.com>,
        Hillf Danton <hdanton@sina.com>
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From:   Valentin Schneider <valentin.schneider@arm.com>
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Date:   Tue, 8 Oct 2019 16:48:35 +0100
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On 08/10/2019 16:30, Vincent Guittot wrote:
[...]
> 
> This is how I plan to get ride of the problem:
> +		if (busiest->group_weight == 1 || sds->prefer_sibling) {
> +			unsigned int nr_diff = busiest->sum_h_nr_running;
> +			/*
> +			 * When prefer sibling, evenly spread running tasks on
> +			 * groups.
> +			 */
> +			env->migration_type = migrate_task;
> +			lsub_positive(&nr_diff, local->sum_h_nr_running);
> +			env->imbalance = nr_diff >> 1;
> +			return;
> +		}
> 

I think this wants a 

/* Local could have more tasks than busiest */

atop the lsub, otherwise yeah that ought to work.