From: David Gibson <dwg@au1.ibm.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: aliguori@us.ibm.com, aik@ozlabs.ru, rusty@rustcorp.com.au,
agraf@suse.de, qemu-devel@nongnu.org,
Sasha Levin <levinsasha928@gmail.com>
Subject: Re: [Qemu-devel] [PATCH] virtio: Make memory barriers be memory barriers
Date: Fri, 2 Sep 2011 10:09:52 +1000 [thread overview]
Message-ID: <20110902000952.GM11906@yookeroo.fritz.box> (raw)
In-Reply-To: <4E5F3AA9.5020804@redhat.com>
On Thu, Sep 01, 2011 at 09:56:25AM +0200, Paolo Bonzini wrote:
> On 09/01/2011 09:37 AM, Sasha Levin wrote:
> >>> -#define wmb() __asm__ __volatile__("": : :"memory")
> >>> + /* TODO: we may also need rmb()s. It hasn't bitten us yet, but.. */
> >>> + #define wmb() __sync_synchronize()
> >
> >That asm directive also implicitly provided a compiler barrier, I could
> ^^^^
>
> only
>
> >find whether __sync_synchronize() provides one as well.
> >
> >Any idea if it does?
>
> Of course, __sync_synchronize() is a stronger barrier. The asm is
> simply not a synchronization primitive.
Good to hear that confirmed, I hadn't checked myself. But then a cpu
memory barrier primitive without a compiler barrier would be an insane
thing to have.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
next prev parent reply other threads:[~2011-09-02 0:39 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-01 6:09 [Qemu-devel] [PATCH] virtio: Make memory barriers be memory barriers David Gibson
2011-09-01 6:47 ` Paolo Bonzini
2011-09-02 0:08 ` David Gibson
2011-09-02 6:49 ` Paolo Bonzini
2011-09-03 11:53 ` Blue Swirl
2011-09-01 7:37 ` Sasha Levin
2011-09-01 7:38 ` Sasha Levin
2011-09-01 7:56 ` Paolo Bonzini
2011-09-02 0:09 ` David Gibson [this message]
2011-09-01 15:30 ` Michael S. Tsirkin
2011-09-01 16:14 ` Paolo Bonzini
2011-09-01 16:34 ` Michael S. Tsirkin
2011-09-01 20:31 ` Paolo Bonzini
2011-09-02 15:45 ` Michael S. Tsirkin
2011-09-03 14:46 ` David Gibson
2011-09-04 9:16 ` Michael S. Tsirkin
2011-09-05 4:43 ` David Gibson
2011-09-05 9:19 ` Michael S. Tsirkin
2011-09-06 3:12 ` David Gibson
2011-09-06 6:55 ` Paolo Bonzini
2011-09-06 9:02 ` David Gibson
2011-09-06 9:28 ` Avi Kivity
2011-09-06 9:35 ` Michael S. Tsirkin
2011-09-06 9:38 ` Paolo Bonzini
2011-09-05 7:41 ` Paolo Bonzini
2011-09-05 8:06 ` Michael S. Tsirkin
2011-09-05 9:42 ` Paolo Bonzini
2011-09-03 16:19 ` Paolo Bonzini
2011-09-04 8:47 ` Michael S. Tsirkin
2011-09-02 0:11 ` David Gibson
2011-09-02 6:11 ` Paolo Bonzini
2011-09-02 15:57 ` Michael S. Tsirkin
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