Re: [PATCH-next 00/23] cgroup/cpuset: Enable runtime update of nohz_full and managed_irq CPUs

[Waiman Long <longman@redhat.com>]

On 6/24/26 2:34 AM, Jing Wu wrote:
> Hi Waiman,
>
> Thomas Gleixner suggested we coordinate, so reaching out directly.
>
> We have been working on a similar feature called Dynamic Housekeeping
> Management (DHM) [1][2][3][4]. The RFC was posted on 2026-02-06, v1 on
> 2026-03-25, and v2 on 2026-04-13 — a week before your series appeared.
> It seems we developed these independently in parallel.
>
> After Thomas's review of DHM v3, we are rebuilding v4 around the
> CPU-by-CPU offline/online hotplug mechanism, which aligns with the
> direction of your series.
>
> There is one key difference in scope worth discussing:
>
>    Your series requires "nohz_full=" to be present at boot (even with
>    an empty CPU list) to opt into runtime updates. DHM targets systems
>    where nohz_full= was never configured at boot — enabling CPU noise
>    isolation purely at runtime without any boot-time setup.
>
>    This requires making the nohz_full infrastructure activatable at
>    runtime for the first time, rather than just extending an already-
>    initialized boot configuration.
>
> Before we start coding v4, a few questions:
>
>    1. Are you planning a v2 of your series? If so, what is your
>       timeline? We want to avoid duplicating effort on the subsystem
>       patches (tick, RCU, genirq).

Yes, I am planning to send out a v2 in a few weeks depending on whether 
I can finish the other works that I am doing right now.


>
>    2. Would you be open to extending your series to cover the
>       "no boot parameter" use case, or do you think it is better kept
>       as a separate series?
The reason to make the v1 series depending on the nohz_full parameter is 
basically a short cut as some code will change its behavior slightly 
depending on if the nohz_full parameter is set. By making it optional, 
we just have to add more code to enable them. It is more work, but 
doable. I will make that optional in the next version, but I probably 
won't have all the needed code other than the essential ones and the 
rests will be handled in a followup patch series.
>
>    3. Are there specific patches in your series where you would welcome
>       our contribution directly?

I have broken down the shutdown callback into separate portions as 
suggested by Thomas. The other major change that I am working on is to 
try to shutdown to only CPUHP_AP_OFFLINE state instead of all the way 
down to CPUHP_OFFLINE. That will require some adjustments to the 
nohz_full related hotplug functions. I have some ideas of what needs to 
be done. However, I haven't looked into RCU yet. I know RCU support 
changing the nocb mask for fully offline CPUs, I will need to find out 
if it possible to do that for partially offline CPUs.

The work has been suspended for a while as I have other works to do. 
Hopefully I can restart it soon to further refresh my memory and we can 
discuss collaboration at that point.

Cheers,
Longman


>
> Happy to collaborate on a unified approach.
>
> [1] DHM RFC (2026-02-06): https://lore.kernel.org/r/20260206-feature-dynamic_isolcpus_dhei-v1-0-00a711eb0c74@gmail.com
> [2] DHM v1  (2026-03-25): https://lore.kernel.org/r/20260325-dhei-v12-final-v1-0-919cca23cadf@gmail.com
> [3] DHM v2  (2026-04-13): https://lore.kernel.org/r/20260413-wujing-dhm-v2-0-06df21caba5d@gmail.com
> [4] DHM v3  (2026-06-18): https://lore.kernel.org/r/20260618-wujing-dhm-v3-0-28f1a4d83b68@gmail.com
> [5] Your series v1 (2026-04-20): https://lore.kernel.org/r/20260421030351.281436-1-longman@redhat.com
>
> Jing Wu <realwujing@gmail.com>
> Qiliang Yuan <yuanql9@chinatelecom.cn>
>