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Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for
From: |
Emilio G. Cota |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics |
Date: |
Tue, 24 May 2016 15:56:09 -0400 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
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
- [Qemu-devel] [PATCH 0/2] atomics: fix small RCU perf. regression + update documentation, Emilio G. Cota, 2016/05/21
- [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics, Emilio G. Cota, 2016/05/21
- Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics, Alex Bennée, 2016/05/22
- Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics, Paolo Bonzini, 2016/05/23
- Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics, Richard Henderson, 2016/05/23
- Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics, Emilio G. Cota, 2016/05/23
- Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics, Paolo Bonzini, 2016/05/24
- Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics,
Emilio G. Cota <=
- Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics, Sergey Fedorov, 2016/05/24
- Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics, Alex Bennée, 2016/05/25
- Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics, Sergey Fedorov, 2016/05/25
[Qemu-devel] [PATCH 2/2] docs/atomics: update atomic_read/set comparison with Linux, Emilio G. Cota, 2016/05/21