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From:   Amit Kucheria <amit.kucheria@linaro.org>
Date:   Thu, 13 Feb 2020 19:09:42 +0530
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Subject: Re: [Patch v9 5/8] sched/fair: update cpu_capacity to reflect thermal pressure
To:     Thara Gopinath <thara.gopinath@linaro.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, ionela.voinescu@arm.com,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Zhang Rui <rui.zhang@intel.com>, qperret@google.com,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Sudeep Holla <sudeep.holla@arm.com>,
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        LKML <linux-kernel@vger.kernel.org>,
        Amit Daniel Kachhap <amit.kachhap@gmail.com>,
        Javi Merino <javi.merino@kernel.org>
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On Wed, Jan 29, 2020 at 4:06 AM Thara Gopinath
<thara.gopinath@linaro.org> wrote:
>
> cpu_capacity initially reflects the maximum possible capacity of a cpu.
> Thermal pressure on a cpu means this maximum possible capacity is
> unavailable due to thermal events. This patch subtracts the average thermal
> pressure for a cpu from its maximum possible capacity so that cpu_capacity
> reflects the actual maximum currently available capacity.

"actual maximum currently available capacity" is quite a mouthful. :-)

"Remaining capacity" or "Effective capacity" anyone?

IIUC, this remaining capacity is NOT the same as the capped/decreased
capacity referred to in patches 1 and 3. The delta capacity (aka
thermal pressure) there refers to the difference between HW max
capacity and thermally throttled capacity.
Here, we also subtract RT/DL utilisation. Is that accurate?


>
> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> ---
>
> v8->v9:
>         - Use thermal_load_avg to read rq->avg_thermal.load_avg.
>
>  kernel/sched/fair.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 5f58c03..d879077 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7753,8 +7753,15 @@ 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(load).
> +        */
>         used = READ_ONCE(rq->avg_rt.util_avg);
>         used += READ_ONCE(rq->avg_dl.util_avg);
> +       used += thermal_load_avg(rq);
>
>         if (unlikely(used >= max))
>                 return 1;
> --
> 2.1.4
>