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.
