From: Will Deacon <will.deacon@arm.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
"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>
Subject: Re: [RFC PATCH v2] memory-barriers: remove smp_mb__after_unlock_lock()
Date: Tue, 18 Aug 2015 09:37:04 +0100 [thread overview]
Message-ID: <20150818083704.GC10301@arm.com> (raw)
In-Reply-To: <1439862655.1763.2.camel@ellerman.id.au>
On Tue, Aug 18, 2015 at 02:50:55AM +0100, Michael Ellerman wrote:
> On Mon, 2015-08-17 at 09:57 +0100, Will Deacon wrote:
> > On Mon, Aug 17, 2015 at 07:15:01AM +0100, Paul E. McKenney wrote:
> > > On Mon, Aug 17, 2015 at 02:06:07PM +1000, Michael Ellerman wrote:
> > > > On Wed, 2015-08-12 at 08:43 -0700, Paul E. McKenney wrote:
> > > > I thought the end result of this thread was that we didn't *need* to change the
> > > > powerpc lock semantics? Or did I read it wrong?
> > > >
> > > > ie. the docs now say that RELEASE+ACQUIRE is not a full barrier, which is
> > > > consistent with our current implementation.
> > >
> > > That change happened about 1.5 years ago, and I thought that the
> > > current discussion was about reversing it, based in part on the
> > > recent powerpc benchmarks of locking primitives with and without the
> > > sync instruction. But regardless, I clearly cannot remove either the
> > > smp_mb__after_unlock_lock() or the powerpc definition of it to be smp_mb()
> > > if powerpc unlock/lock is not strengthened.
> >
> > Yup. Peter and I would really like to get rid of smp_mb__after_unlock_lock
> > entirely, which would mean strengthening the ppc spinlocks. Moving the
> > barrier primitive into RCU is a good step to prevent more widespread usage
> > of the barrier, but we'd really like to go further if the performance impact
> > is deemed acceptable (which is what this thread is about).
>
> OK, sorry for completely missing the point, too many balls in the air here.
No problem!
> I'll do some benchmarks and see what we come up with.
Thanks, that sounds great. FWIW, there are multiple ways of implementing
the patch (i.e. whether you strengthen lock or unlock). I had a crack at
something here, but it's not tested:
http://marc.info/?l=linux-arch&m=143758379023849&w=2
Will
next prev parent reply other threads:[~2015-08-18 8:37 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
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 [this message]
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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