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

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Date:   Fri, 15 Nov 2019 18:34:19 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Valentin Schneider <valentin.schneider@....com>
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 Fri, 15 Nov 2019 at 18:10, Valentin Schneider
<valentin.schneider@....com> wrote:
>
> 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.

Thanks for the pointer and deep diving in the email threads