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

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Date:   Tue, 8 Oct 2019 19:55:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com, pauld@...hat.com,
        valentin.schneider@....com, srikar@...ux.vnet.ibm.com,
        quentin.perret@....com, dietmar.eggemann@....com,
        Morten.Rasmussen@....com, hdanton@...a.com
Subject: Re: [PATCH v3 04/10] sched/fair: rework load_balance

On Thu, Sep 19, 2019 at 09:33:35AM +0200, Vincent Guittot wrote:
> +	if (busiest->group_type == group_asym_packing) {
> +		/*
> +		 * In case of asym capacity, we will try to migrate all load to
> +		 * the preferred CPU.
> +		 */
> +		env->balance_type = migrate_load;
>  		env->imbalance = busiest->group_load;
>  		return;
>  	}

I was a bit surprised with this; I sorta expected a migrate_task,1 here.

The asym_packing thing has always been a nr_running issue to me. If
there is something to run, we should run on as many siblings/cores as
possible, but preferably the 'highest' ranked siblings/cores.