From: "H. Peter Anvin" <hpa@zytor.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Rob Landley <rob@landley.net>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, Arnd Bergmann <arnd@arndb.de>,
Andrew Morton <akpm@linux-foundation.org>,
David Howells <dhowells@redhat.com>,
Akinobu Mita <akinobu.mita@gmail.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Herbert Xu <herbert@gondor.hengli.com.au>,
Stephen Rothwell <sfr@canb.auug.org.au>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arch@vger.kernel.org, Gleb Natapov <gleb@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, Avi Kivity <avi@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] bitops: add _local bitops
Date: Wed, 09 May 2012 09:24:41 -0700 [thread overview]
Message-ID: <4FAA9A49.8080900@zytor.com> (raw)
In-Reply-To: <20120509154734.GB20867@redhat.com>
On 05/09/2012 08:47 AM, Michael S. Tsirkin wrote:
>
> By the way, clear_bit on x86 does not seem to contain
> an optimization barrier - is my reading correct?
> Lock prefix does not affect the compiler, right?
Yes, as it clearly states in the comment:
* clear_bit() is atomic and may not be reordered. However, it does
* not contain a memory barrier, so if it is used for locking purposes,
* you should call smp_mb__before_clear_bit() and/or
smp_mb__after_clear_bit()
* in order to ensure changes are visible on other processors.
There is clear_bit_unlock() which has the barrier semantics.
-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:[~2012-05-09 16:24 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-09 13:45 [PATCH] bitops: add _local bitops Michael S. Tsirkin
2012-05-09 14:03 ` H. Peter Anvin
2012-05-09 15:06 ` Michael S. Tsirkin
2012-05-09 15:43 ` Michael S. Tsirkin
2012-05-09 15:44 ` H. Peter Anvin
2012-05-09 15:47 ` Michael S. Tsirkin
2012-05-09 16:24 ` H. Peter Anvin [this message]
2012-05-09 16:36 ` Michael S. Tsirkin
2012-05-09 16:45 ` H. Peter Anvin
2012-05-09 16:55 ` Michael S. Tsirkin
2012-05-09 14:06 ` Arnd Bergmann
2012-05-09 14:17 ` Avi Kivity
2012-05-09 19:19 ` Andrew Morton
2012-05-09 19:23 ` H. Peter Anvin
2012-05-09 20:07 ` Michael S. Tsirkin
2012-05-09 20:10 ` H. Peter Anvin
2012-05-09 20:12 ` Michael S. Tsirkin
2012-05-10 9:26 ` Avi Kivity
2012-05-10 23:02 ` Benjamin Herrenschmidt
2012-05-10 17:38 ` Rob Landley
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