linux-kernel - Re: [PATCH] sched: write better comments for weight calculations

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Message-ID: <CAJWu+oqitEv_e_gD7VCbqop3nBu1iwiU0jNaKkEudj4Omoh=iA@mail.gmail.com>
Date:   Wed, 22 Mar 2017 12:28:01 -0700
From:   Joel Fernandes <joelaf@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Juri Lelli <Juri.Lelli@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] sched: write better comments for weight calculations

On Wed, Mar 22, 2017 at 10:55 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Mar 22, 2017 at 09:25:02AM -0700, Joel Fernandes wrote:
>> On Wed, Mar 22, 2017 at 7:18 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>> > On Fri, Mar 10, 2017 at 12:47:43PM -0800, Joel Fernandes wrote:
>> >> This patch rewrites comments related task priorities and CPU usage
>> >> along with an example to show how it works.
>> >
>> > To what purpose? Bigger word count?
>>
>> The intention is to improve the comments to make it more
>> understandable (the weight calculations, factor of 1.25 etc).
>>
>> On reading through the comments the first time, I felt they could be
>> improved. Is your concern more about the addition of an example
>> increasing the word-count? Perhaps you'd rather this be added to
>> Documentation/ instead?
>
> It might just be verbiage; I sometimes have trouble condensing text.
> That is; some people need repetition, I get stuck trying to figure out
> if its saying the same or not.
>
> In any case; if you want to clarify where the 1.25 comes from, maybe do
> an abstract example, instead of an explicit one?
>
>  -10% = .9, +10% = 1.1 -> 1.1/.9 = 1.(2) ~ 1.25
>
> Or, starting with the weight thing:
>
> .45 = wa / (wa+wb) -> .45 (wa+wb) = wa ->
>                       .45wa + .45wb = wa ->
>                       .45wb = .55wa ->
>                       wb/wa = .55/.45 = 1.(2) ~ 1.25
>
> That's actually simpler to follow no?
>
> Now IIRC the whole thing is backwards anyway, we started with 1.25 and
> got the ~10% from there.

Yes we could condense it further and explain it without using an
explicit example. I will work on a better patch along these lines.

Thanks,
Joel