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

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Message-ID: <20170322175541.culjydvydyzy4dza@hirez.programming.kicks-ass.net>
Date:   Wed, 22 Mar 2017 18:55:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joel Fernandes <joelaf@...gle.com>
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 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.