Re: [PATCH 01/15] sched/isolation: Support dynamic allocation for housekeeping masks

Qiliang Yuan
2026-03-30T11:44:20Z

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Hi Peter,

On Wed, Mar 25, 2026 at 02:57:07PM +0100, Peter Zijlstra wrote:
> I think I asked this a while ago; why do we have more than one mask?
> What is the actual purpose of being able to separate RCU from Timers?

That's a fair point. For the vast majority of use cases (like NOHZ_FULL),
these masks are indeed identical and should be updated as a single unit.

The original motivation for separation was to allow extreme fine-tuning in
HFT environments—for example, offloading RCU callbacks to keep a core
mostly clean but allowing pinned timers for specific localized
telemetry/monitoring.

However, I acknowledge this adds significant complexity. In V13, I will
unify these into a single "Global Housekeeping Mask" by default to
simplify the configuration space, while keeping the underlying notifier
infrastructure flexible enough for future specialized needs.