Re: [PATCH v3 08/13] genirq: Add explicit housekeeping callback for managed IRQ migration

[Jing Wu <realwujing@gmail.com>]

On Thu, Jun 18 2026 at 22:27, Thomas Gleixner wrote:
> While this series might work for you by some definition of "works",
> it's broken beyond repair [...]
> Please coordinate with Waiman or whoever is working on it at RH right now.

Thank you for the detailed review. I want to clarify the timeline and
highlight a key distinction before proceeding with v4.

DHM was posted as RFC on 2026-02-06 [1], v1 on 2026-03-25 [2], and v2
on 2026-04-13 [3]. Waiman Long's series was posted on 2026-04-20 [4],
seven days after DHM v2. The development appears to have been parallel.

More importantly, DHM and Waiman's series differ in a key requirement:
Waiman's series requires "nohz_full=" to be present at boot (even with
an empty CPU list) to opt into runtime updates. DHM's goal is to enable
CPU noise isolation at runtime on systems where no nohz_full= was
configured at boot — a use case his series does not cover.

That said, I fully accept the architectural feedback: the on-the-fly
subsystem modification approach in v3 is wrong, and v4 should use the
CPU hotplug machinery.

We are open to coordinating with Waiman on a unified approach that
covers both use cases. Before starting v4, two questions:

  1. Is the "no boot parameter required" use case worth pursuing
     independently, or should it be folded into Waiman's series?

  2. For the hotplug path: is CPU-by-CPU offline/online the expected
     mechanism, given that you rejected the cpuhp_offline_cb() bulk
     approach in Waiman's v1?

[1] https://lore.kernel.org/r/20260206-feature-dynamic_isolcpus_dhei-v1-0-00a711eb0c74@gmail.com
[2] https://lore.kernel.org/r/20260325-dhei-v12-final-v1-0-919cca23cadf@gmail.com
[3] https://lore.kernel.org/r/20260413-wujing-dhm-v2-0-06df21caba5d@gmail.com
[4] https://lore.kernel.org/r/20260421030351.281436-1-longman@redhat.com

Jing Wu <realwujing@gmail.com>