From: Paolo Bonzini <pbonzini@redhat.com>
To: "Emilio G. Cota" <cota@braap.org>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 4/4] membarrier: add --enable-membarrier
Date: Thu, 22 Mar 2018 09:57:49 +0100 [thread overview]
Message-ID: <6f939e5d-ad2f-62a3-9e2f-22f6bd17bc94@redhat.com> (raw)
In-Reply-To: <20180322012937.GB16453@flamenco>
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
next prev parent reply other threads:[~2018-03-22 8:57 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-09 13:29 [Qemu-devel] [PATCH 0/4] Optionally use membarrier system call for RCU Paolo Bonzini
2018-03-09 13:29 ` [Qemu-devel] [PATCH 1/4] rcutorture: remove synchronize_rcu from readers Paolo Bonzini
2018-03-09 13:29 ` [Qemu-devel] [PATCH 2/4] rcu: make memory barriers more explicit Paolo Bonzini
2018-03-09 13:29 ` [Qemu-devel] [PATCH 3/4] membarrier: introduce qemu/sys_membarrier.h Paolo Bonzini
2018-03-09 13:29 ` [Qemu-devel] [PATCH 4/4] membarrier: add --enable-membarrier Paolo Bonzini
2018-03-22 1:29 ` Emilio G. Cota
2018-03-22 8:57 ` Paolo Bonzini [this message]
2018-03-09 13:37 ` [Qemu-devel] [PATCH 0/4] Optionally use membarrier system call for RCU no-reply
2018-03-22 1:03 ` Emilio G. Cota
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