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Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for
From: |
Sergey Fedorov |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics |
Date: |
Tue, 24 May 2016 22:59:57 +0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 |
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
Best,
Sergey
- [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, 2016/05/24
- Re: [Qemu-devel] [PATCH 1/2] atomics: do not use __atomic primitives for RCU atomics,
Sergey Fedorov <=
- 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