From: "H. Peter Anvin" <hpa@zytor.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: mingo@elte.hu, tglx@linutronix.de,
"eric.dumazet@gmail.com" <eric.dumazet@gmail.com>,
luca@luca-barbieri.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] ix86: atomic64 assembly improvements
Date: Wed, 18 Jan 2012 08:36:21 -0800 [thread overview]
Message-ID: <4F16F505.8040809@zytor.com> (raw)
In-Reply-To: <4F16E41B020000780006D7A5@nat28.tlf.novell.com>
On 01/18/2012 06:24 AM, Jan Beulich wrote:
> The cmpxchg8b variants of "set" and "xchg" are really identical, and
> hence don't need to be repeated: %ebx and %ecx don't need to be copied
> into %eax and %edx respectively (this is only necessary when desiring
> to only read the stored value), and the LOCK prefix should also be used
> in "set" (other than the comment that is now being removed was saying,
> there is - to my knowledge - no *architectural* guarantee that aligned
> 64-bit writes would always be carried out atomically).
EWHAT?
It's atomic in the same way a MOV is atomic.
The CPU could, in fact, execute the locked version at all if the
unlocked version didn't behave like that.
Unless you have a specific instance where you think this might be
violated, please let me know.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
next prev parent reply other threads:[~2012-01-18 16:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-18 14:24 [PATCH 2/2] ix86: atomic64 assembly improvements Jan Beulich
2012-01-18 16:36 ` H. Peter Anvin [this message]
2012-01-18 16:50 ` Jan Beulich
2012-01-18 17:47 ` H. Peter Anvin
2012-01-19 9:18 ` Jan Beulich
2012-01-19 14:44 ` H. Peter Anvin
2012-01-19 14:50 ` Jan Beulich
2012-01-19 14:55 ` H. Peter Anvin
2012-01-19 14:59 ` H. Peter Anvin
2012-01-19 15:11 ` Jan Beulich
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