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-v1-0-00a711eb0...@gmail.com
[2] DHM v1 (2026-03-25):
https://lore.kernel.org/r/[email protected]
[3] DHM v2 (2026-04-13):
https://lore.kernel.org/r/[email protected]
[4] DHM v3 (2026-06-18):
https://lore.kernel.org/r/[email protected]
[5] Your series v1 (2026-04-20):
https://lore.kernel.org/r/[email protected]
Jing Wu <[email protected]>
Qiliang Yuan <[email protected]>
