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From: Paolo Bonzini <pbonzini@redhat.com>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: aliguori@us.ibm.com, aik@ozlabs.ru, rusty@rustcorp.com.au,
	agraf@suse.de, qemu-devel@nongnu.org,
	David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [Qemu-devel] [PATCH] virtio: Make memory barriers be memory barriers
Date: Thu, 01 Sep 2011 09:56:25 +0200	[thread overview]
Message-ID: <4E5F3AA9.5020804@redhat.com> (raw)
In-Reply-To: <1314862622.26813.6.camel@lappy>

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.

Paolo

  parent reply	other threads:[~2011-09-01  7:56 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 [this message]
2011-09-02  0:09     ` David Gibson
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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