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Subject: Re: [GIT PULL] scheduler changes for v5.5
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Ingo Molnar <mingo@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Mel Gorman <mgorman@suse.de>, Ben Segall <bsegall@google.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Juri Lelli <juri.lelli@redhat.com>
References: <20191125125944.GA22218@gmail.com>
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 <CAHk-=wjV6CGaVXYoWvQER4_xmFdX2eTBSYf+6WhcgAx+K9M+Og@mail.gmail.com>
From:   Valentin Schneider <valentin.schneider@arm.com>
Message-ID: <ea914edf-4674-368a-f32c-d4eeeabea703@arm.com>
Date:   Mon, 25 Nov 2019 16:50:37 +0000
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On 25/11/2019 16:48, Linus Torvalds wrote:
> On Mon, Nov 25, 2019 at 5:49 AM Valentin Schneider
> <valentin.schneider@arm.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.
> 

Fair enough, lesson learned, sorry for the noise.