Messages in this thread | | | Date | Wed, 28 Jul 2021 14:12:05 -0400 (EDT) | From | Mathieu Desnoyers <> | Subject | Re: [PATCH v2 rcu 04/18] rcu: Weaken ->dynticks accesses and updates |
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----- On Jul 28, 2021, at 1:58 PM, Linus Torvalds torvalds@linux-foundation.org wrote:
> On Wed, Jul 28, 2021 at 10:37 AM Paul E. McKenney <paulmck@kernel.org> wrote: >> >> +/* >> + * Increment the current CPU's rcu_data structure's ->dynticks field >> + * with ordering. Return the new value. >> + */ >> +static noinstr unsigned long rcu_dynticks_inc(int incby) >> +{ >> + return arch_atomic_add_return(incby, this_cpu_ptr(&rcu_data.dynticks)); >> +} > > Maybe inline? > > But more I reacted to how we sadly don't have percpu atomics. They'd > be fairly easy to add on x86, but I guess it's not a huge deal.
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.
I must be missing something subtle because AFAIU those are already available. Those per-cpu atomics don't provide any memory ordering though, which may be why those are not used here.
Thanks,
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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