From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: heiko.carstens@de.ibm.com, horms@verge.net.au,
linux-kernel@vger.kernel.org, rpjday@mindspring.com, ak@suse.de,
netdev@vger.kernel.org, cfriesen@nortel.com,
akpm@linux-foundation.org, torvalds@linux-foundation.org,
Nick Piggin <nickpiggin@yahoo.com.au>,
linux-arch@vger.kernel.org, jesper.juhl@gmail.com, zlynx@acm.org,
schwidefsky@de.ibm.com, Chris Snook <csnook@redhat.com>,
davem@davemloft.net, wensong@linux-vs.org, wjiang@resilience.com,
David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 6/24] make atomic_read() behave consistently on frv
Date: Wed, 15 Aug 2007 12:59:15 -0700 [thread overview]
Message-ID: <20070815195915.GL9645@linux.vnet.ibm.com> (raw)
In-Reply-To: <369924c4b3132a4b06258b7ac81b1006@kernel.crashing.org>
On Wed, Aug 15, 2007 at 09:46:55PM +0200, Segher Boessenkool wrote:
> >>>Well if there is only one memory location involved, then smp_rmb()
> >>>isn't
> >>>going to really do anything anyway, so it would be incorrect to use
> >>>it.
> >>
> >>rmb() orders *any* two reads; that includes two reads from the same
> >>location.
> >
> >If the two reads are to the same location, all CPUs I am aware of
> >will maintain the ordering without need for a memory barrier.
>
> That's true of course, although there is no real guarantee for that.
A CPU that did not provide this property ("cache coherence") would be
most emphatically reviled. So we are pretty safe assuming that CPUs
will provide it.
Thanx, Paul
next prev parent reply other threads:[~2007-08-15 19:59 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-08-09 13:41 [PATCH 6/24] make atomic_read() behave consistently on frv Chris Snook
2007-08-09 16:54 ` Chris Snook
2007-08-10 9:23 ` David Howells
2007-08-10 19:54 ` Chris Snook
2007-08-11 0:54 ` Herbert Xu
2007-08-11 4:29 ` Paul E. McKenney
2007-08-13 5:15 ` Herbert Xu
2007-08-13 6:03 ` Paul E. McKenney
2007-08-14 5:34 ` Nick Piggin
2007-08-14 7:26 ` Herbert Xu
2007-08-14 17:01 ` Paul E. McKenney
2007-08-14 22:01 ` Arnd Bergmann
2007-08-14 22:43 ` Paul E. McKenney
2007-08-15 13:29 ` Arnd Bergmann
2007-08-15 15:06 ` Michael Buesch
2007-08-15 13:30 ` Nick Piggin
2007-08-15 20:15 ` Paul E. McKenney
2007-08-16 1:09 ` Nick Piggin
2007-08-16 2:27 ` Paul E. McKenney
2007-08-11 8:47 ` David Howells
2007-08-13 6:44 ` Chris Snook
2007-08-14 5:42 ` Nick Piggin
2007-08-15 18:51 ` Segher Boessenkool
2007-08-15 19:18 ` Paul E. McKenney
2007-08-15 19:46 ` Segher Boessenkool
2007-08-15 19:59 ` Paul E. McKenney [this message]
2007-08-15 20:13 ` Segher Boessenkool
2007-08-15 20:38 ` Paul E. McKenney
2007-08-15 21:15 ` Segher Boessenkool
2007-08-16 1:20 ` Nick Piggin
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