From: Andrea Parri <andrea.parri@amarulasolutions.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@linux.ibm.com>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
Alan Stern <stern@rowland.harvard.edu>,
Boqun Feng <boqun.feng@gmail.com>,
Nicholas Piggin <npiggin@gmail.com>,
David Howells <dhowells@redhat.com>,
Jade Alglave <j.alglave@ucl.ac.uk>,
Luc Maranget <luc.maranget@inria.fr>,
Akira Yokosawa <akiyks@gmail.com>,
Daniel Lustig <dlustig@nvidia.com>
Subject: Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo
Date: Wed, 20 Feb 2019 14:17:30 +0100 [thread overview]
Message-ID: <20190220131730.GB3215@andrea> (raw)
In-Reply-To: <20190220095659.GA17578@brain-police>
On Wed, Feb 20, 2019 at 09:57:00AM +0000, Will Deacon wrote:
> On Wed, Feb 20, 2019 at 10:26:04AM +0100, Peter Zijlstra wrote:
> > On Tue, Feb 19, 2019 at 06:01:17PM -0800, Paul E. McKenney wrote:
> > > On Tue, Feb 19, 2019 at 11:57:37PM +0100, Andrea Parri wrote:
> > > > Remove this subtle (and, AFAICT, unused) ordering: we can add it back,
> > > > if necessary, but let us not encourage people to rely on this thing.
> > > >
> > > > For example, the following "exists" clause can be satisfied with this
> > > > change:
> > > >
> > > > C dep-rfi
> > > >
> > > > { }
> > > >
> > > > P0(int *x, int *y)
> > > > {
> > > > WRITE_ONCE(*x, 1);
> > > > smp_store_release(y, 1);
> > > > }
> > > >
> > > > P1(int *x, int *y, int *z)
> > > > {
> > > > int r0;
> > > > int r1;
> > > > int r2;
> > > >
> > > > r0 = READ_ONCE(*y);
> > > > WRITE_ONCE(*z, r0);
> > > > r1 = smp_load_acquire(z);
> > > > r2 = READ_ONCE(*x);
> > > > }
> > > >
> > > > exists (1:r0=1 /\ 1:r2=0)
> > >
> > > Any objections? If I don't hear any in a couple days, I will apply this.
> >
> > IIUC you cannot build hardware that allows the above, so why would we
> > allow it?
>
> Agreed. Maybe the intention was to make the dependency between the read of
> *y and the write of *z on P1 a control dependency instead? That's certainly
> allowed on arm64.
No no, I did mean dep (= addr | data). As you remarked, control dep.
aren't going to work here. I expanded on this in my reply to peterz.
Andrea
>
> Will
next prev parent reply other threads:[~2019-02-20 13:17 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-19 22:57 [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo Andrea Parri
2019-02-19 22:57 ` Andrea Parri
2019-02-20 2:01 ` Paul E. McKenney
2019-02-20 2:01 ` Paul E. McKenney
2019-02-20 9:26 ` Peter Zijlstra
2019-02-20 9:26 ` Peter Zijlstra
2019-02-20 9:57 ` Will Deacon
2019-02-20 9:57 ` Will Deacon
2019-02-20 13:17 ` Andrea Parri [this message]
2019-02-20 13:17 ` Andrea Parri
2019-02-20 13:14 ` Andrea Parri
2019-02-20 13:14 ` Andrea Parri
2019-02-20 13:27 ` Peter Zijlstra
2019-02-20 13:27 ` Peter Zijlstra
2019-02-22 11:21 ` Andrea Parri
2019-02-22 11:21 ` Andrea Parri
2019-02-22 13:00 ` Peter Zijlstra
2019-02-22 13:00 ` Peter Zijlstra
2019-02-25 17:55 ` Paul E. McKenney
2019-02-25 17:55 ` Paul E. McKenney
2019-02-26 9:21 ` Peter Zijlstra
2019-02-26 9:21 ` Peter Zijlstra
2019-02-26 9:30 ` Peter Zijlstra
2019-02-26 9:30 ` Peter Zijlstra
2019-02-26 10:45 ` Peter Zijlstra
2019-02-26 10:45 ` Peter Zijlstra
2019-02-26 11:21 ` Peter Zijlstra
2019-02-26 11:21 ` Peter Zijlstra
2019-02-26 11:25 ` Peter Zijlstra
2019-02-26 11:25 ` Peter Zijlstra
2019-02-26 11:30 ` Peter Zijlstra
2019-02-26 11:30 ` Peter Zijlstra
2019-02-26 11:38 ` Borislav Petkov
2019-02-26 11:38 ` Borislav Petkov
2019-02-26 13:49 ` Peter Zijlstra
2019-02-26 13:49 ` Peter Zijlstra
2019-02-26 14:28 ` Paul E. McKenney
2019-02-26 14:28 ` Paul E. McKenney
2019-02-26 14:47 ` Peter Zijlstra
2019-02-26 14:47 ` Peter Zijlstra
2019-02-26 15:39 ` Paul E. McKenney
2019-02-26 15:39 ` Paul E. McKenney
2019-02-26 14:56 ` Akira Yokosawa
2019-02-26 14:56 ` Akira Yokosawa
2019-02-26 15:04 ` Paul E. McKenney
2019-02-26 15:04 ` Paul E. McKenney
2019-02-26 15:09 ` Akira Yokosawa
2019-02-26 15:09 ` Akira Yokosawa
2019-02-26 15:04 ` Peter Zijlstra
2019-02-26 15:04 ` Peter Zijlstra
2019-03-06 15:46 ` Akira Yokosawa
2019-03-06 15:46 ` Akira Yokosawa
2019-03-06 16:58 ` Peter Zijlstra
2019-03-06 16:58 ` Peter Zijlstra
2019-03-06 17:26 ` Paul E. McKenney
2019-03-06 17:26 ` Paul E. McKenney
2019-03-06 17:24 ` Paul E. McKenney
2019-03-06 17:24 ` Paul E. McKenney
2019-03-02 15:27 ` Akira Yokosawa
2019-03-02 15:27 ` Akira Yokosawa
2019-03-04 16:09 ` Paul E. McKenney
2019-03-04 16:09 ` Paul E. McKenney
2019-02-20 13:41 ` Will Deacon
2019-02-20 13:41 ` Will Deacon
2019-02-20 15:30 ` Alan Stern
2019-02-20 15:30 ` Alan Stern
2019-02-20 15:22 ` Alan Stern
2019-02-20 15:22 ` Alan Stern
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