On Tue, May 24, 2016 at 09:08:01 +0200, Paolo Bonzini wrote:
> On 23/05/2016 19:09, Emilio G. Cota wrote:
> > PS. And really equating smp_wmb/rmb to release/acquire as we have under
> > #ifdef __ATOMIC is hard to justify, other than to please tsan.
>
> That only makes a difference on arm64, right?
>
> acquire release rmb wmb
> x86 -- -- -- --
> power lwsync lwsync lwsync lwsync
> armv7 dmb dmb dmb dmb
> arm64 dmb ishld dmb ish dmb ishld dmb ishst
> ia64 -- -- -- --
Yes. I now see why we're defining rmb/wmb based on acquire/release:
it's quite convenient given that the compiler provides them, and
the (tiny) differences in practice are not worth the trouble of
adding asm for them. So I take back my comment =)
The gains of getting rid of the consume barrier from atomic_rcu_read
are clear though; updated patch to follow.
Thanks,
Emilio
