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Subject: Re: [Patch v5 1/6] sched/pelt.c: Add support to track thermal
 pressure
To:     Thara Gopinath <thara.gopinath@linaro.org>, mingo@redhat.com,
        peterz@infradead.org, ionela.voinescu@arm.com,
        vincent.guittot@linaro.org, rui.zhang@intel.com,
        edubezval@gmail.com, qperret@google.com
Cc:     linux-kernel@vger.kernel.org, amit.kachhap@gmail.com,
        javi.merino@kernel.org, daniel.lezcano@linaro.org
References: <1572979786-20361-1-git-send-email-thara.gopinath@linaro.org>
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From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <6e2b2a11-834d-a0ee-a386-1edc624a8050@arm.com>
Date:   Wed, 6 Nov 2019 13:50:21 +0100
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On 05/11/2019 19:49, Thara Gopinath wrote:
> Extrapolating on the exisiting framework to track rt/dl utilization using

s/exisiting/existing

> pelt signals, add a similar mechanism to track thermal pressure. The
> difference here from rt/dl utilization tracking is that, instead of
> tracking time spent by a cpu running a rt/dl task through util_avg,
> the average thermal pressure is tracked through load_avg. This is
> because thermal pressure signal is weighted "delta" capacity
> and is not binary(util_avg is binary). "delta capacity" here
> means delta between the actual capacity of a cpu and the decreased
> capacity a cpu due to a thermal event.
> In order to track average thermal pressure, a new sched_avg variable
> avg_thermal is introduced. Function update_thermal_load_avg can be called
> to do the periodic bookeeping (accumulate, decay and average)

s/bookeeping/bookkeeping

> of the thermal pressure.
> 
> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> ---
>  kernel/sched/pelt.c  | 13 +++++++++++++
>  kernel/sched/pelt.h  |  7 +++++++
>  kernel/sched/sched.h |  1 +
>  3 files changed, 21 insertions(+)
> 
> diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c
> index a96db50..3821069 100644
> --- a/kernel/sched/pelt.c
> +++ b/kernel/sched/pelt.c
> @@ -353,6 +353,19 @@ int update_dl_rq_load_avg(u64 now, struct rq *rq, int running)
>  	return 0;
>  }

Minor thing: There are function headers for rt_rq, dl_rq and irq. rt_rq
even explains that 'load_avg and runnable_load_avg are not supported and
meaningless.' Could you do something similar for thermal here? It's not
self-explanatory why we track load_avg, runnable_load_avg and util_avg
for thermal but only use load_avg.

> +int update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity)
> +{
> +	if (___update_load_sum(now, &rq->avg_thermal,
> +			       capacity,
> +			       capacity,
> +			       capacity)) {
> +		___update_load_avg(&rq->avg_thermal, 1, 1);
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +

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