Received-SPF: pass (google.com: domain of linux-kernel+bounces-190736-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Mon, 27 May 2024 09:37:40 -0400
From: Alan Stern <stern@rowland.harvard.edu>
To: Andrea Parri <parri.andrea@gmail.com>
Cc: Hernan Ponce de Leon <hernan.poncedeleon@huaweicloud.com>,
  will@kernel.org, peterz@infradead.org, boqun.feng@gmail.com,
  npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk,
  luc.maranget@inria.fr, paulmck@kernel.org, akiyks@gmail.com,
  dlustig@nvidia.com, joel@joelfernandes.org, linux-kernel@vger.kernel.org,
  linux-arch@vger.kernel.org, jonas.oberhauser@huaweicloud.com
Subject: Re: [PATCH] tools/memory-model: Document herd7 (internal)
 representation
Message-ID: <79b55c10-dd06-4947-8545-20ffeb324bc6@rowland.harvard.edu>
References: <20240524151356.236071-1-parri.andrea@gmail.com>
 <1a3c892c-903e-8fd3-24a6-2454c2a55302@huaweicloud.com>
 <ZlSKYA/Y/daiXzfy@andrea>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <ZlSKYA/Y/daiXzfy@andrea>

On Mon, May 27, 2024 at 03:28:00PM +0200, Andrea Parri wrote:
> > > +    |                smp_store_mb | W[once] ->po F[mb]                        |
> > 
> > I expect this one to be hard-coded in herd7 source code, but I cannot find
> > it. Can you give me a pointer?
> 
> smp_store_mb() is currently mapped to { __store{once}(X,V); __fence{mb}; } in
> the .def file, so it's semantically equivalent to "WRITE_ONCE(); smp_mb();".

Why don't we use this approach for all the value-returning full-barrier 
RMW operations?  That would immediately solve the issue of the 
special-purpose code in herd7, leaving only the matter of how to 
annotate failed RMW operations.

Alan