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Message-ID: <139acc54-d24c-5437-7a9d-fa2438fffba4@joelfernandes.org>
Date:   Thu, 22 Jun 2023 09:11:17 -0400
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Subject: Re: [PATCH 08/15] sched: Commit to EEVDF
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To:     Ingo Molnar <mingo@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>, vincent.guittot@linaro.org,
        linux-kernel@vger.kernel.org, juri.lelli@redhat.com,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, corbet@lwn.net,
        qyousef@layalina.io, chris.hyser@oracle.com,
        patrick.bellasi@matbug.net, pjt@google.com, pavel@ucw.cz,
        qperret@google.com, tim.c.chen@linux.intel.com, joshdon@google.com,
        timj@gnu.org, kprateek.nayak@amd.com, yu.c.chen@intel.com,
        youssefesmat@chromium.org, efault@gmx.de, tglx@linutronix.de
References: <20230531115839.089944915@infradead.org>
 <20230531124604.137187212@infradead.org> <20230616212353.GA628850@google.com>
 <ZJQ4A2Jm4VoGMKbl@gmail.com>
From:   Joel Fernandes <joel@joelfernandes.org>
In-Reply-To: <ZJQ4A2Jm4VoGMKbl@gmail.com>
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On 6/22/23 08:01, Ingo Molnar wrote:
> 
> * Joel Fernandes <joel@joelfernandes.org> wrote:
> 
>> On Wed, May 31, 2023 at 01:58:47PM +0200, Peter Zijlstra wrote:
>>> EEVDF is a better defined scheduling policy, as a result it has less
>>> heuristics/tunables. There is no compelling reason to keep CFS around.
>>>
>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>>> ---
>>>   kernel/sched/debug.c    |    6
>>>   kernel/sched/fair.c     |  465 +++---------------------------------------------
>>
>> Whether EEVDF helps us improve our CFS latency issues or not, I do like the
>> merits of this diffstat alone and the lesser complexity and getting rid of
>> those horrible knobs is kinda nice.
> 
> To to be fair, the "removal" in this patch is in significant part an
> artifact of the patch series itself, because first EEVDF bits get added by
> three earlier patches, in parallel to CFS:
> 
>   kernel/sched/fair.c     |  137 +++++++++++++++++++++++++++++++++++++++++++++++++--
>   kernel/sched/fair.c     |  162 +++++++++++++++++++++++++++++++++++++-----------
>   kernel/sched/fair.c     |  338 +++++++++++++++++++++++++++++++++++++++++-------
> 
> ... and then we remove the old CFS policy code in this 'commit to EEVDF' patch:
> 
>   kernel/sched/fair.c     |  465 +++---------------------------------------------
> 
> The combined diffstat is close to 50% / 50% balanced:
> 
>   kernel/sched/fair.c              | 1105 ++++++++++++++++++--------------------
> 
> But having said that, I do agree that EEVDF as submitted by Peter is better
> defined, with fewer heuristics, which is an overall win - so no complaints
> from me!

Agreed, thank you for correcting me on the statistics.

  - Joel