Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 12 Jul 2018 22:24:57 +0200
From:   Andrea Parri <andrea.parri@amarulasolutions.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Will Deacon <will.deacon@arm.com>,
        Akira Yokosawa <akiyks@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Daniel Lustig <dlustig@nvidia.com>,
        David Howells <dhowells@redhat.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
        Nick Piggin <npiggin@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] tools/memory-model: Add extra ordering for locks and
 remove it for ordinary release/acquire
Message-ID: <20180712202457.GA4767@andrea>
References: <20180712134821.GT2494@hirez.programming.kicks-ass.net>
 <Pine.LNX.4.44L0.1807121236470.1306-100000@iolanthe.rowland.org>
 <20180712172838.GU3593@linux.vnet.ibm.com>
 <20180712180511.GP2476@hirez.programming.kicks-ass.net>
 <CA+55aFxwez8zSa2f2GpcaAkFX27Vt-s0nWdd0mZ6yGM8ipCR0A@mail.gmail.com>
 <20180712195242.GA4170@andrea>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20180712195242.GA4170@andrea>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Jul 12, 2018 at 09:52:42PM +0200, Andrea Parri wrote:
> On Thu, Jul 12, 2018 at 11:10:58AM -0700, Linus Torvalds wrote:
> > On Thu, Jul 12, 2018 at 11:05 AM Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > The locking pattern is fairly simple and shows where RCpc comes apart
> > > from expectation real nice.
> > 
> > So who does RCpc right now for the unlock-lock sequence? Somebody
> > mentioned powerpc. Anybody else?
> 
> powerpc have RCtso (and RCpc) but not RCsc unlock-lock, according to the
> following indeed original terminology:
> 
>  - RCsc unlock-lock MUST ORDER:
> 
>   a) the WRITE and the READ below:
> 
>       WRITE x=1
>       UNLOCK s
>       LOCK s
>       READ y
> 
>       as in a store-buffering test;
> 
>   b) the two WRITEs below:
> 
>       WRITE x=1
>       UNLOCK s
>       LOCK s
>       WRITE y=1
> 
>       as in a message-passing test;
> 
>   c) the two READs below:
> 
>       READ x
>       UNLOCK s
>       LOCK s
>       READ y
> 
>       as in a message-passing test;
> 
>   d) the READ and the WRITE below:
> 
>       READ x
>       UNLOCK s
>       LOCK s
>       WRITE y
> 
>       as in a load-buffering test;
> 
>  - RCtso unlock-lock MUST ORDER b), c), d) above.
> 
>  - RCpc unlock-lock MUST ORDER none of the above.
> 
> AFAICT, all arch _in_ the current implementation have RCtso unlock-lock.
> 
> 
> > 
> > How nasty would be be to make powerpc conform? I will always advocate
> > tighter locking and ordering rules over looser ones..
> 
> A simple answer is right above (place a sync somewhere in the sequence);
> for benchmark results, I must defer...

Sorry, not sure why but I did intend "conform to RCsc" here.


> 
>   Andrea
> 
> 
> > 
> >            Linus