[PATCH 17/19] srcu: Optimize SRCU-fast-updown for arm64

[Mathieu Desnoyers]

On 2025-11-03 14:17, Paul E. McKenney wrote:
[...]
>> This is effectively a use of split-counters, but the split
>> is across concurrency handling mechanisms rather than across
>> CPUs.
> 
> Ah, got it, thank you!  But we would need an additional softirq counter,
> correct?

Fundamentally it depends on how you want to split frequent vs infrequent
accesses.

If the fast-paths you care about are all in thread context, then you
only need to split between percpu ops vs atomic counters. The per-thread
accesses would use percpu ops, and all the rest use atomics. The "all
the rest" can cover everything else including softirqs, irq, and nmis.

> 
> I will keep this in my back pocket in case Catalin's and Yicong's prefetch
> trick turns out to be problematic, and again, thank you!

You're welcome! :)

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com