linux-kernel - Re: [Patch v6 5/7] sched/fair: update cpu

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Message-ID: <20191223175213.GB31446@arm.com>
Date:   Mon, 23 Dec 2019 17:52:13 +0000
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Thara Gopinath <thara.gopinath@...aro.org>
Cc:     mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        rui.zhang@...el.com, qperret@...gle.com, daniel.lezcano@...aro.org,
        viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
        amit.kachhap@...il.com, javi.merino@...nel.org,
        amit.kucheria@...durent.com
Subject: Re: [Patch v6 5/7] sched/fair: update cpu_capacity to reflect
 thermal pressure

On Wednesday 11 Dec 2019 at 23:11:46 (-0500), Thara Gopinath wrote:
> cpu_capacity relflects the maximum available capacity of a cpu. Thermal
> pressure on a cpu means this maximum available capacity is reduced. This
> patch reduces the average thermal pressure for a cpu from its maximum

Maybe we can introduce two terms here: maximum possible capacity and
maximum currently available capacity.
I think using these two terms the message can become more clear:

cpu_capacity initially reflects the maximum possible capacity of a cpu
(capacity orig). Thermal pressure on a cpu means this maximum
possible capacity of a cpu is not available due to thermal events.
This patch subtracts the average thermal pressure for a cpu from the
cpu's maximum possible capacity so that cpu_capacity reflects the
actual maximum currently available capacity.

Kind regards,
Ionela.

> available capacity so that cpu_capacity reflects the actual
> available capacity.
> 
> Signed-off-by: Thara Gopinath <thara.gopinath@...aro.org>
> ---
>  kernel/sched/fair.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e12a375..4840655 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7725,8 +7725,15 @@ static unsigned long scale_rt_capacity(struct sched_domain *sd, int cpu)
>  	if (unlikely(irq >= max))
>  		return 1;
>  
> +	/*
> +	 * avg_rt.util avg and avg_dl.util track binary signals
> +	 * (running and not running) with weights 0 and 1024 respectively.
> +	 * avg_thermal.load_avg tracks thermal pressure and the weighted
> +	 * average uses the actual delta max capacity.
> +	 */
>  	used = READ_ONCE(rq->avg_rt.util_avg);
>  	used += READ_ONCE(rq->avg_dl.util_avg);
> +	used += READ_ONCE(rq->avg_thermal.load_avg);
>  
>  	if (unlikely(used >= max))
>  		return 1;
> -- 
> 2.1.4
>