Re: [PATCH 2/2] tools/memory-model: Add write ordering by release-acquire and by locks

From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Alan Stern <stern@rowland.harvard.edu>,
	Will Deacon <will.deacon@arm.com>,
	LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	David Howells <dhowells@redhat.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Luc Maranget <luc.maranget@inria.fr>,
	Nicholas Piggin <npiggin@gmail.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2] tools/memory-model: Add write ordering by release-acquire and by locks
Date: Mon, 25 Jun 2018 10:29:23 +0200	[thread overview]
Message-ID: <20180625082923.GA5808@andrea> (raw)
In-Reply-To: <20180625073229.GR2494@hirez.programming.kicks-ass.net>

On Mon, Jun 25, 2018 at 09:32:29AM +0200, Peter Zijlstra wrote:
> 
> I have yet to digest the rest of the discussion, however:
> 
> On Fri, Jun 22, 2018 at 02:09:04PM -0400, Alan Stern wrote:
> > The LKMM uses the same CAT code for acquire/release and lock/unlock.
> > (In essence, it considers a lock to be an acquire and an unlock to be a
> > release; everything else follows from that.)  Treating one differently
> > from the other in these tests would require some significant changes.
> > It wouldn't be easy.
> 
> That is problematic, acquire+release are very much simpler operations
> than lock+unlock.
> 
> At the very least, lock includes a control-dependency, where acquire
> does not.

I don't see how this is relevant here; roughly, "if something is guaranteed
by a control-dependency, that is also guaranteed by an acquire".  Right? ;)

  Andrea