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SubjectRe: [PATCH v2 rcu 04/18] rcu: Weaken ->dynticks accesses and updates
----- On Jul 28, 2021, at 2:32 PM, Linus Torvalds torvalds@linux-foundation.org wrote:

> On Wed, Jul 28, 2021 at 11:12 AM Mathieu Desnoyers
> <mathieu.desnoyers@efficios.com> wrote:
>>
>> Are the percpu atomics you have in mind different from what is found in
>> Documentation/core-api/this_cpu_ops.rst ?
>>
>> Namely this_cpu_add_return(pcp, val) in this case.
>
> Nope.
>
> Those are only "CPU-atomic", ie atomic wrt interrupts etc.
>
> The RCU code wants SMP-atomic, and it's mainly that we *could* do the
> addressing more efficiently.

OK, so combining the addressing tricks of this_cpu operations with
smp-atomic operations (e.g. LOCK prefix on x86). It may indeed become
worthwhile given enough users, and fast enough atomic operations.

Thanks,

Mathieu

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

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