linux-kernel - Re: [PATCH v2] sched/uclamp: Fix overzealous type replacement

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Message-ID: <2dce8a83-b358-d975-bf43-8088b3bc5557@arm.com>
Date:   Fri, 15 Nov 2019 17:10:05 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dietmar Eggemann <Dietmar.Eggemann@....com>,
        Tejun Heo <tj@...nel.org>,
        Patrick Bellasi <patrick.bellasi@...bug.net>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Qais Yousef <qais.yousef@....com>
Subject: Re: [PATCH v2] sched/uclamp: Fix overzealous type replacement

On 15/11/2019 14:29, Valentin Schneider wrote:
> On 15/11/2019 14:07, Vincent Guittot wrote:
>>> -static inline enum uclamp_id uclamp_none(enum uclamp_id clamp_id)
>>> +static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
>>
>> Out of curiosity why uclamp decided to use unsigned int to manipulate
>> utilization instead of unsigned long which is the type of util_avg ?
>>
> 
> I didn't stare at the discussion much, but I think it stems from the
> design choices behind struct uclamp_se: everything is crammed in an unsigned
> int bitfield. Let me see if I can find some relevant mails.
> 

So I think a relevant mail is:

https://lore.kernel.org/lkml/20180912174236.GB24106@hirez.programming.kicks-ass.net/

Other than that, the uclamp_se.value field was 'int' in v1 and has been
'unsigned int' for all following versions. uclamp_bucket.value is a bitfield
of an 'unsigned long' just because we want more headroom for the tasks count,
AFAICT.