Sergey Fedorov <serge.f...@gmail.com> writes: > On 24/05/16 22:56, Emilio G. Cota wrote: >> 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. > > However, maybe it's not such a pain to maintain an optimized version for > AArch64 in assembly :P
Please don't. The advantage of the builtins is they are known by things like tsan. > > Best, > Sergey -- Alex Bennée
