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

[Qiliang Yuan]

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.