linux-kernel - Re: [PATCH v2 1/4] sched/uclamp: Make uclamp_util

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Message-ID: <2a244463-8010-ccf4-dc33-80831265ba9a@arm.com>
Date:   Wed, 4 Dec 2019 17:15:23 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Quentin Perret <qperret@...gle.com>,
        Qais Yousef <qais.yousef@....com>,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH v2 1/4] sched/uclamp: Make uclamp_util_*() helpers use and
 return UL values

On 04/12/2019 16:12, Vincent Guittot wrote:
> On Wed, 4 Dec 2019 at 17:03, Valentin Schneider
> <valentin.schneider@....com> wrote:
>>
>> On 04/12/2019 15:22, Vincent Guittot wrote:
>>>> @@ -2303,15 +2303,15 @@ static inline void cpufreq_update_util(struct rq *rq, unsigned int flags) {}
>>>>  unsigned int uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id);
>>>
>>> Why not changing uclamp_eff_value to return unsigned long too ? The
>>> returned value represents a utilization to be compared with other
>>> utilization value
>>>
>>
>> IMO uclamp_eff_value() is a simple accessor to uclamp_se.value
>> (unsigned int), which is why I didn't want to change its return type.
>> I see it as being the task equivalent of rq->uclamp[clamp_id].value, IOW
>> "give me the uclamp value for that clamp index". It just happens to be a
>> bit more intricate for tasks than for rqs.
> 
> But then you have to take care of casting the returned value in
> several places here and in patch 3
> 

True. I'm not too hot on having to handle rq clamp values
(rq->uclamp[x].value) and task clamp values (uclamp_eff_value())
differently (cast one but not the other), but I don't feel *too* strongly
about this, so if you want I can do that change for v3.

>>
>> uclamp_util() & uclamp_util_with() do explicitly return a utilization,
>> so here it makes sense (in my mind, that is) to return UL.