linux-kernel - Re: [PATCH v3 04/10] sched/fair: rework load

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Message-ID: <20191008173910.GB22902@worktop.programming.kicks-ass.net>
Date:   Tue, 8 Oct 2019 19:39:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, Phil Auld <pauld@...hat.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        Hillf Danton <hdanton@...a.com>
Subject: Re: [PATCH v3 04/10] sched/fair: rework load_balance

On Tue, Oct 08, 2019 at 05:30:02PM +0200, 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'm thinking the max_t(long, 0, ...); variant reads a lot simpler and
really _should_ work given that -fno-strict-overflow / -fwrapv mandates
2s complement.