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Re: [Qemu-devel] [PATCH 4/4] membarrier: add --enable-membarrier
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 4/4] membarrier: add --enable-membarrier |
Date: |
Thu, 22 Mar 2018 09:57:49 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 |
On 22/03/2018 02:29, Emilio G. Cota wrote:
> It is indeed hard to see a large impact on performance given the
> large size of our critical sections. But hey, rcu_read_unlock
> goes down from 0.24% to 0.08% of execution time when booting
> aarch64 linux!
I expect something a little better than 0.15% from virtio, especially
once I re-enable MemoryRegionCache in 2.13.
>> + int main(void) {
>> + syscall(__NR_membarrier, MEMBARRIER_CMD_QUERY, 0);
>> + syscall(__NR_membarrier, MEMBARRIER_CMD_SHARED, 0);
>> + }
>
> I think we should also check here that MEMBARRIER_CMD_SHARED is
> actually supported;
Checking run-time constraints at compile-time is a bit pointless. My
idea was to add a third mode where the choice is done at run-time, but
that wouldn't have made 2.12.
Paolo
- [Qemu-devel] [PATCH 0/4] Optionally use membarrier system call for RCU, Paolo Bonzini, 2018/03/09
- [Qemu-devel] [PATCH 4/4] membarrier: add --enable-membarrier, Paolo Bonzini, 2018/03/09
- [Qemu-devel] [PATCH 2/4] rcu: make memory barriers more explicit, Paolo Bonzini, 2018/03/09
- [Qemu-devel] [PATCH 3/4] membarrier: introduce qemu/sys_membarrier.h, Paolo Bonzini, 2018/03/09
- [Qemu-devel] [PATCH 1/4] rcutorture: remove synchronize_rcu from readers, Paolo Bonzini, 2018/03/09
- Re: [Qemu-devel] [PATCH 0/4] Optionally use membarrier system call for RCU, no-reply, 2018/03/09
- Re: [Qemu-devel] [PATCH 0/4] Optionally use membarrier system call for RCU, Emilio G. Cota, 2018/03/21