linux-kernel - Re: [PATCH v6.12] sched/fair: Block delayed tasks on throttled hierarchy during dequeue

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Message-ID: <fe9320d4-9da0-4de8-8e1e-ec03ecf582a1@amd.com>
Date: Wed, 15 Oct 2025 11:57:19 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: Sasha Levin <sashal@...nel.org>, <stable@...r.kernel.org>, Matt Fleming
	<matt@...dmodwrite.com>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra
	<peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot
	<vincent.guittot@...aro.org>, <linux-kernel@...r.kernel.org>, "Dietmar
 Eggemann" <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, "Valentin
 Schneider" <vschneid@...hat.com>, <kernel-team@...udflare.com>, Matt Fleming
	<mfleming@...udflare.com>, Oleg Nesterov <oleg@...hat.com>, John Stultz
	<jstultz@...gle.com>, Chris Arges <carges@...udflare.com>
Subject: Re: [PATCH v6.12] sched/fair: Block delayed tasks on throttled
 hierarchy during dequeue

Hello Greg,

On 10/15/2025 11:44 AM, Greg Kroah-Hartman wrote:
>> Greg, Sasha,
>>
>> This fix cleanly applies on top of v6.16.y and v6.17.y stable kernels
>> too when cherry-picked from v6.12.y branch (or with 'git am -3'). Let me
>> know if you would like me to send a seperate patch for each.
>>
>> As mentioned above, the upstream fixes this as a part of larger feature
>> and we would only like these bits backported. If there are any future
>> conflicts in this area during backporting, I would be more than happy to
>> help out resolve them.
> 
> Why not just backport all of the mainline changes instead?  As I say a
> lot, whenever we do these "one off" changes, it's almost always wrong
> and causes problems over the years going forward as other changes around
> the same area can not be backported either.
> 
> So please, try to just backport the original commits.

Peter was in favor of backporting just the necessary bits in
https://lore.kernel.org/all/20250929103836.GK3419281@noisy.programming.kicks-ass.net/

Backporting the whole of per-task throttle feature is lot more heavy
handed with the core changes adding:

 include/linux/sched.h |   5 +
 kernel/sched/core.c   |   3 +
 kernel/sched/fair.c   | 451 ++++++++++++++++++++++++------------------
 kernel/sched/pelt.h   |   4 +-
 kernel/sched/sched.h  |   7 +-
 5 files changed, 274 insertions(+), 196 deletions(-)

And a few more fixes that will add to the above before v6.18. I'll defer
to Peter to decide the best course of action.

-- 
Thanks and Regards,
Prateek