netdev - Re: [PATCH 00/33 v6] cpuset/isolation: Honour kthreads preferred affinity

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Message-ID: <2857c203-96e5-4bf9-b19c-7a80b009cce2@redhat.com>
Date: Mon, 12 Jan 2026 20:49:11 -0500
From: Waiman Long <llong@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>, Waiman Long <llong@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
 Phil Auld <pauld@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Lai Jiangshan <jiangshanlai@...il.com>, Danilo Krummrich <dakr@...nel.org>,
 Catalin Marinas <catalin.marinas@....com>, Michal Koutny <mkoutny@...e.com>,
 netdev@...r.kernel.org, Roman Gushchin <roman.gushchin@...ux.dev>,
 linux-block@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
 Eric Dumazet <edumazet@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Ingo Molnar <mingo@...hat.com>,
 Chen Ridong <chenridong@...wei.com>, cgroups@...r.kernel.org,
 linux-pci@...r.kernel.org, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "David S . Miller" <davem@...emloft.net>, Vlastimil Babka <vbabka@...e.cz>,
 Marco Crivellari <marco.crivellari@...e.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>,
 "Rafael J . Wysocki" <rafael@...nel.org>,
 Johannes Weiner <hannes@...xchg.org>, Simon Horman <horms@...nel.org>,
 Shakeel Butt <shakeel.butt@...ux.dev>, linux-mm@...ck.org,
 Jakub Kicinski <kuba@...nel.org>, linux-arm-kernel@...ts.infradead.org,
 Gabriele Monaco <gmonaco@...hat.com>, Muchun Song <muchun.song@...ux.dev>,
 Will Deacon <will@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Chen Ridong <chenridong@...weicloud.com>
Subject: Re: [PATCH 00/33 v6] cpuset/isolation: Honour kthreads preferred
 affinity

On 1/12/26 5:09 PM, Frederic Weisbecker wrote:
> Le Mon, Jan 12, 2026 at 01:23:40PM -0500, Waiman Long a écrit :
>> On 1/1/26 5:13 PM, Frederic Weisbecker wrote:
>>> Hi,
>>>
>>> The kthread code was enhanced lately to provide an infrastructure which
>>> manages the preferred affinity of unbound kthreads (node or custom
>>> cpumask) against housekeeping constraints and CPU hotplug events.
>>>
>>> One crucial missing piece is cpuset: when an isolated partition is
>>> created, deleted, or its CPUs updated, all the unbound kthreads in the
>>> top cpuset are affine to _all_ the non-isolated CPUs, possibly breaking
>>> their preferred affinity along the way
>>>
>>> Solve this with performing the kthreads affinity update from cpuset to
>>> the kthreads consolidated relevant code instead so that preferred
>>> affinities are honoured.
>>>
>>> The dispatch of the new cpumasks to workqueues and kthreads is performed
>>> by housekeeping, as per the nice Tejun's suggestion.
>>>
>>> As a welcome side effect, HK_TYPE_DOMAIN then integrates both the set
>>> from isolcpus= and cpuset isolated partitions. Housekeeping cpumasks are
>>> now modifyable with specific synchronization. A big step toward making
>>> nohz_full= also mutable through cpuset in the future.
>>>
>>> Changes since v5:
>>>
>>> * Add more tags
>>>
>>> * Fix leaked destroy_work_on_stack() (Zhang Qiao, Waiman Long)
>>>
>>> * Comment schedule_drain_work() synchronization requirement (Tejun)
>>>
>>> * s/Revert of/Inverse of (Waiman Long)
>>>
>>> * Remove housekeeping_update() needless (for now) parameter (Chen Ridong)
>>>
>>> * Don't propagate housekeeping_update() failures beyond allocations (Waiman Long)
>>>
>>> * Whitespace cleanup (Waiman Long)
>>>
>>>
>>> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
>>> 	kthread/core-v6
>>>
>>> HEAD: 811e87ca8a0a1e54eb5f23e71896cb97436cccdc
>>>
>>> Happy new year,
>>> 	Frederic
>> I don't see any major issue with this v6 version. There may be some minor
>> issues that can be cleaned up later. Now the issue is which tree should this
>> series go to as it touches a number of different subsystems with different
>> maintainers.
> It indeed crosses many subsystems. I would be fine if anybody takes it but
> nobody volunteered so far.
>
> The main purpose is to fix kthreads affinity (HK_TYPE_DOMAIN handling cpuset is
> a bonus). And since I made the pull request myself to Linus when I introduced
> kthreads managed affinity, I guess I could reiterate with this patchset. I
> already pushed it to linux-next.
>
> But if anybody wants to pull that to another tree, that's fine, just tell me
> so that we synchronize to avoid duplication on linux-next.
>
> Thanks.

Good to know as I am wondering where it will go. So you are going to 
push that directly to Linus.

Cheers,
Longman