linux-kernel - Re: [GIT PULL] scheduler changes for v5.5

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Message-ID: <CAHk-=wjV6CGaVXYoWvQER4_xmFdX2eTBSYf+6WhcgAx+K9M+Og@mail.gmail.com>
Date:   Mon, 25 Nov 2019 08:48:46 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Mel Gorman <mgorman@...e.de>, Ben Segall <bsegall@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [GIT PULL] scheduler changes for v5.5

On Mon, Nov 25, 2019 at 5:49 AM Valentin Schneider
<valentin.schneider@....com> wrote:
>
> On 25/11/2019 12:59, Ingo Molnar wrote:
>
> So I really don't want to be labeled as "that annoying scheduler PR guy",
> but some patches in Vincent's rework should be squashed to avoid being
> performance bisection honeypots.
>
> > Vincent Guittot (14):
> >       sched/fair: Remove meaningless imbalance calculation
> >       sched/fair: Rework load_balance()
>
> These two ^ (were split for ease of reviewing, [1])
>
> >       sched/fair: Rework find_idlest_group()
> >       sched/fair: Fix rework of find_idlest_group()
>
> And these two ^ (Mel voiced similar concerns at [2])

If they were split for ease of reviewing, then they should be split in
the history too.

I worry a lot less about some possible (temporary!) performance dip
than about a hard bug, and if the code is easier to review in two
steps then it's going to be easier to find the bug in two steps too.

                     Linus