From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will.deacon@arm.com>
Cc: Peter Hurley <peter@hurleysoftware.com>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul McKenney <paulmck@linux.vnet.ibm.com>
Subject: Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock()
Date: Mon, 13 Jul 2015 17:56:06 +0200 [thread overview]
Message-ID: <20150713155606.GC19282@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150713142418.GF2632@arm.com>
On Mon, Jul 13, 2015 at 03:24:18PM +0100, Will Deacon wrote:
> On Mon, Jul 13, 2015 at 02:09:50PM +0100, Peter Hurley wrote:
> > On 07/13/2015 08:15 AM, Will Deacon wrote:
> > > smp_mb__after_unlock_lock is used to promote an UNLOCK + LOCK sequence
> > > into a full memory barrier.
> > >
> > > However:
> > >
> > > - This ordering guarantee is already provided without the barrier on
> > > all architectures apart from PowerPC
> > >
> > > - The barrier only applies to UNLOCK + LOCK, not general
> > > RELEASE + ACQUIRE operations
> >
> > I'm unclear what you mean here: do you mean
> > A) a memory barrier is not required between RELEASE M + ACQUIRE N when you
> > want to maintain distinct order between those operations on all arches
> > (with the possible exception of PowerPC), or,
> > B) no one is using smp_mb__after_unlock_lock() in that way right now.
>
> My understanding is (B), but Peter and I don't seem to agree yet!
> I'll tighten up the text once we reach a conclusion.
I'm fairly sure (but I've not looked) that nobody does in fact rely on
this.
So I'm in agreement with B, and I'm quibbling on what exactly A means
;-)
next prev parent reply other threads:[~2015-07-13 15:56 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-13 12:15 [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock() Will Deacon
2015-07-13 13:09 ` Peter Hurley
2015-07-13 14:24 ` Will Deacon
2015-07-13 15:56 ` Peter Zijlstra [this message]
2015-07-13 13:11 ` Peter Zijlstra
2015-07-13 14:09 ` Will Deacon
2015-07-13 14:21 ` Will Deacon
2015-07-13 15:54 ` Peter Zijlstra
2015-07-13 17:50 ` Will Deacon
2015-07-13 20:20 ` Paul E. McKenney
2015-07-13 22:23 ` Peter Zijlstra
2015-07-13 23:04 ` Paul E. McKenney
2015-07-14 10:04 ` Will Deacon
2015-07-14 12:45 ` Paul E. McKenney
2015-07-14 12:51 ` Will Deacon
2015-07-14 14:00 ` Paul E. McKenney
2015-07-14 14:12 ` Will Deacon
2015-07-14 19:31 ` Paul E. McKenney
2015-07-15 1:38 ` Paul E. McKenney
2015-07-15 10:51 ` Will Deacon
2015-07-15 13:12 ` Paul E. McKenney
2015-07-24 11:31 ` Will Deacon
2015-07-24 15:30 ` Paul E. McKenney
2015-08-12 13:44 ` Will Deacon
2015-08-12 15:43 ` Paul E. McKenney
2015-08-12 17:59 ` Paul E. McKenney
2015-08-13 10:49 ` Will Deacon
2015-08-13 13:10 ` Paul E. McKenney
2015-08-17 4:06 ` Michael Ellerman
2015-08-17 6:15 ` Paul E. McKenney
2015-08-17 8:57 ` Will Deacon
2015-08-18 1:50 ` Michael Ellerman
2015-08-18 8:37 ` Will Deacon
2015-08-20 9:45 ` Michael Ellerman
2015-08-20 15:56 ` Will Deacon
2015-08-26 0:27 ` Paul E. McKenney
2015-08-26 4:06 ` Michael Ellerman
2015-07-13 18:23 ` Paul E. McKenney
2015-07-13 19:41 ` Peter Hurley
2015-07-13 20:16 ` Paul E. McKenney
2015-07-13 22:15 ` Peter Zijlstra
2015-07-13 22:43 ` Benjamin Herrenschmidt
2015-07-14 8:34 ` Peter Zijlstra
2015-07-13 22:53 ` Paul E. McKenney
2015-07-13 22:37 ` Benjamin Herrenschmidt
2015-07-13 22:31 ` Benjamin Herrenschmidt
2015-07-14 10:16 ` Will Deacon
2015-07-15 3:06 ` Michael Ellerman
2015-07-15 10:44 ` Will Deacon
2015-07-16 2:00 ` Michael Ellerman
2015-07-16 5:03 ` Benjamin Herrenschmidt
2015-07-16 5:14 ` Benjamin Herrenschmidt
2015-07-16 15:11 ` Paul E. McKenney
2015-07-16 22:54 ` Benjamin Herrenschmidt
2015-07-17 9:32 ` Will Deacon
2015-07-17 10:15 ` Peter Zijlstra
2015-07-17 12:40 ` Paul E. McKenney
2015-07-17 22:14 ` Benjamin Herrenschmidt
2015-07-20 13:39 ` Will Deacon
2015-07-20 13:48 ` Paul E. McKenney
2015-07-20 13:56 ` Will Deacon
2015-07-20 21:18 ` Benjamin Herrenschmidt
2015-07-22 16:49 ` Will Deacon
2015-07-22 16:49 ` Will Deacon
2015-07-22 16:49 ` Will Deacon
2015-09-01 2:57 ` Paul Mackerras
2015-07-15 14:18 ` Paul E. McKenney
2015-07-16 1:34 ` Michael Ellerman
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