Re: [PATCH v2 11/13] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups

From: Sai Gurrappadi <sgurrappadi@nvidia.com>
To: Morten Rasmussen <morten.rasmussen@arm.com>,
	<peterz@infradead.org>, <mingo@redhat.com>
Cc: <dietmar.eggemann@arm.com>, <yuyang.du@intel.com>,
	<vincent.guittot@linaro.org>, <mgalbraith@suse.de>,
	<linux-kernel@vger.kernel.org>,
	Peter Boonstoppel <pboonstoppel@nvidia.com>
Subject: Re: [PATCH v2 11/13] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups
Date: Thu, 23 Jun 2016 14:20:48 -0700	[thread overview]
Message-ID: <576C52B0.5080504@nvidia.com> (raw)
In-Reply-To: <1466615004-3503-12-git-send-email-morten.rasmussen@arm.com>

Hi Morten,

On 06/22/2016 10:03 AM, Morten Rasmussen wrote:

[...]

>  
> +/*
> + * group_smaller_cpu_capacity: Returns true if sched_group sg has smaller
> + * per-cpu capacity than sched_group ref.
> + */
> +static inline bool
> +group_smaller_cpu_capacity(struct sched_group *sg, struct sched_group *ref)
> +{
> +	return sg->sgc->max_capacity * capacity_margin <
> +						ref->sgc->max_capacity * 1024;
> +}
> +
>  static inline enum
>  group_type group_classify(struct sched_group *group,
>  			  struct sg_lb_stats *sgs)
> @@ -6892,6 +6903,19 @@ static bool update_sd_pick_busiest(struct lb_env *env,
>  	if (sgs->avg_load <= busiest->avg_load)
>  		return false;
>  
> +	if (!(env->sd->flags & SD_ASYM_CPUCAPACITY))
> +		goto asym_packing;
> +
> +	/* Candidate sg has no more than one task per cpu and has
> +	 * higher per-cpu capacity. Migrating tasks to less capable
> +	 * cpus may harm throughput. Maximize throughput,
> +	 * power/energy consequences are not considered.
> +	 */
> +	if (sgs->sum_nr_running <= sgs->group_weight &&
> +	    group_smaller_cpu_capacity(sds->local, sg))
> +		return false;
> +
> +asym_packing:

What about the case where IRQ/RT work reduces the capacity of some of these bigger CPUs? sgc->max_capacity might not necessarily capture that case.

Thanks,
-Sai