linux-kernel - Re: [Patch v8 4/7] sched/fair: Enable periodic update of average thermal pressure

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Message-ID: <aabc0d05-6092-7e50-9758-acab30d3c434@arm.com>
Date:   Mon, 27 Jan 2020 13:09:12 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Zhang Rui <rui.zhang@...el.com>,
        Quentin Perret <qperret@...gle.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        viresh kumar <viresh.kumar@...aro.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Amit Kachhap <amit.kachhap@...il.com>,
        Javi Merino <javi.merino@...nel.org>,
        Amit Kucheria <amit.kucheria@...durent.com>
Subject: Re: [Patch v8 4/7] sched/fair: Enable periodic update of average
 thermal pressure

On 24/01/2020 16:45, Vincent Guittot wrote:
> On Fri, 24 Jan 2020 at 16:37, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>>
>> On 17/01/2020 16:39, Vincent Guittot wrote:
>>> On Fri, 17 Jan 2020 at 15:55, Peter Zijlstra <peterz@...radead.org> wrote:
>>>>
>>>> On Fri, Jan 17, 2020 at 02:22:51PM +0100, Vincent Guittot wrote:
>>>>> On Thu, 16 Jan 2020 at 16:15, Peter Zijlstra <peterz@...radead.org> wrote:

[...]

>> The 'now' argument is one thing but why not:
>>
>> -int update_thermal_load_avg(u64 now, struct rq *rq, u64 capacity)
>> +int update_thermal_load_avg(u64 now, struct rq *rq)
>>  {
>> +       u64 capacity = arch_cpu_thermal_pressure(cpu_of(rq));
>> +
>>         if (___update_load_sum(now, &rq->avg_thermal,
>>
>> This would make the call-sites __update_blocked_others() and
>> task_tick(_fair)() cleaner.
> 
> I prefer to keep the capacity as argument. This is more aligned with
> others that provides the value of the signal to apply
> 
>>
>> I guess the argument is not to pollute pelt.c. But it already contains
> 
> you've got it. I don't want to pollute the pelt.c file with things not
> related to pelt but thermal as an example.
> 
>> arch_scale_[freq|cpu]_capacity() for irq.

But isn't arch_cpu_thermal_pressure() not exactly the same as
arch_scale_cpu_capacity() and arch_scale_freq_capacity()?

All of them are defined by default within the scheduler code
[include/linux/sched/topology.h or kernel/sched/sched.h] and can be
overwritten by arch code with a fast implementation (e.g. returning a
per-cpu variable).

So why is using arch_scale_freq_capacity() and arch_scale_cpu_capacity()
in update_irq_load_avg [kernel/sched/pelt.c] and update_rq_clock_pelt()
[kernel/sched/pelt.h] OK but arch_cpu_thermal_pressure() in
update_thermal_load_avg() [kernel/sched/pelt.c] not?

Shouldn't arch_cpu_thermal_pressure() not be called
arch_scale_thermal_capacity() to highlight the fact that those three
functions are doing the same thing, scaling capacity by something (cpu,
frequency or thermal)?