Re: [RFC][PATCH 5/5] percpu-rwsem: Optimize readers and reduce global impact

[Linus Torvalds]

On Fri, May 29, 2015 at 1:09 PM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> Doesn't it need mb() before "state = readers_slow" to ensure
> "release" semantics?

Please don't do any mb() at all. Just do smp_store_release() if
release semantics is what you want.

Basically, strive to avoid "smp_mb()" at all costs. It's insanely
expensive compared to pretty much all other serialization
alternatives.

(And try to make sure to pair it with smp_load_acquire() on the other
side for things to make sense)

                  Linus
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