Date: Mon, 28 Nov 2016 17:01:24 +0000
From: Matt Fleming <matt@codeblueprint.co.uk>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org,
        Morten.Rasmussen@arm.com, dietmar.eggemann@arm.com,
        kernellwp@gmail.com, yuyang.du@intel.com, umgwanakikbuti@gmail.com
Subject: Re: [PATCH 1/2 v2] sched: fix find_idlest_group for fork
Message-ID: <20161128170124.GA20785@codeblueprint.co.uk>
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On Fri, 25 Nov, at 04:34:32PM, Vincent Guittot wrote:
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index aa47589..820a787 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5463,13 +5463,19 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
>  	 * utilized systems if we require spare_capacity > task_util(p),
>  	 * so we allow for some task stuffing by using
>  	 * spare_capacity > task_util(p)/2.
> +	 * spare capacity can't be used for fork because the utilization has
> +	 * not been set yet as it need to get a rq to init the utilization
>  	 */
> +	if (sd_flag & SD_BALANCE_FORK)
> +		goto no_spare;
> +
>  	if (this_spare > task_util(p) / 2 &&
>  	    imbalance*this_spare > 100*most_spare)
>  		return NULL;
>  	else if (most_spare > task_util(p) / 2)
>  		return most_spare_sg;
>  
> +no_spare:
>  	if (!idlest || 100*this_load < imbalance*min_load)
>  		return NULL;
>  	return idlest;

It's only a minor comment, but would you be opposed to calling this
label 'skip_spare' to indicate that spare capacity may exist, but
we're not going to make use of it?