From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Will Deacon <will.deacon@arm.com>
Cc: 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, 14 Jul 2015 07:00:14 -0700 [thread overview]
Message-ID: <20150714140014.GD3717@linux.vnet.ibm.com> (raw)
In-Reply-To: <20150714125146.GJ16213@arm.com>
On Tue, Jul 14, 2015 at 01:51:46PM +0100, Will Deacon wrote:
> Hi Paul,
>
> On Tue, Jul 14, 2015 at 01:45:40PM +0100, Paul E. McKenney wrote:
> > On Tue, Jul 14, 2015 at 11:04:29AM +0100, Will Deacon wrote:
> > > Given that RCU is currently the only user of this barrier, how would you
> > > feel about making the barrier local to RCU and not part of the general
> > > memory-barrier API?
> >
> > In theory, no objection. Your thought is to leave the definitions where
> > they are, mark them as being used only by RCU, and removing mention from
> > memory-barriers.txt? Or did you have something else in mind?
>
> Actually, I was thinking of defining them in an RCU header file with an
> #ifdef CONFIG_POWERPC for the smb_mb() version. Then you could have a big
> comment describing the semantics, or put that in an RCU Documentation file
> instead of memory-barriers.txt.
>
> That *should* then mean we notice anybody else trying to use the barrier,
> because they'd need to send patches to either add something equivalent
> or move the definition out again.
My concern with this approach is that someone putting together a new
architecture might miss this. That said, this approach certainly would
work for the current architectures.
> > > My main reason for proposing its removal is because I don't want to see
> > > it being used (incorrectly) all over the place to order the new RELEASE
> > > and ACQUIRE operations I posted separately, at which point we have to try
> > > fixing up all the callers or retrofitting some semantics. It doesn't help
> > > that memory-barriers.txt lumps things like LOCK and ACQUIRE together,
> > > whereas this barrier is currently only intended to be used in conjunction
> > > with the former.
> >
> > Heh! That lumping was considered to be a feature at the time. ;-)
>
> Oh, I'm sure it was added with good intentions!
And we all know which road is paved with good intentions! ;-)
Thanx, Paul
next prev parent reply other threads:[~2015-07-14 14:00 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 [this message]
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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