From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: David Howells <dhowells@redhat.com>,
linux-kernel@vger.kernel.org, mingo@kernel.org,
jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org,
edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com
Subject: Re: [PATCH tip/core/rcu 01/21] doc: READ_ONCE() now implies smp_barrier_depends()
Date: Mon, 4 Dec 2017 14:15:01 -0800 [thread overview]
Message-ID: <20171204221501.GH7829@linux.vnet.ibm.com> (raw)
In-Reply-To: <20171204215448.GY3326@worktop>
On Mon, Dec 04, 2017 at 10:54:48PM +0100, Peter Zijlstra wrote:
> On Mon, Dec 04, 2017 at 10:52:15AM -0800, Paul E. McKenney wrote:
> > On Mon, Dec 04, 2017 at 03:38:56PM +0000, David Howells wrote:
> > > Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> > >
> > > > - Q = READ_ONCE(P); smp_read_barrier_depends(); D = READ_ONCE(*Q);
> > > > + Q = READ_ONCE(P); D = READ_ONCE(*Q);
> > > >
> > > > the CPU will issue the following memory operations:
> > > >
> > > > Q = LOAD P, D = LOAD *Q
> > >
> > > The CPU may now issue two barriers in addition to the loads, so should we show
> > > this? E.g.:
> > >
> > > Q = LOAD P, BARRIER, D = LOAD *Q, BARRIER
> >
> > Good point! How about as shown in the updated patch below?
>
> Humm, I thought the idea was to completely remove read_barrier_depends
> from the lkmm and memory-barriers.txt, making it an Alpha implementation
> detail.
That was indeed my hope, but a too-abrupt departure of DEC Alpha seemed
to be causing some confusion, so I jumped on David's suggested change. My
hope now is to slowly remove mention of DEC Alpha from the documentation.
Hmmm... Maybe we need an LWN article on how we are weaning the memory
model from its historical DEC Alpha influences? That might get the word
out more effectively.
Thanx, Paul
next prev parent reply other threads:[~2017-12-04 22:15 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-01 19:50 [PATCH tip/core/rcu 0/21] De-emphasize {smp_,}read_barrier_depends Paul E. McKenney
2017-12-01 19:50 ` [PATCH tip/core/rcu 01/21] doc: READ_ONCE() now implies smp_barrier_depends() Paul E. McKenney
2017-12-01 19:50 ` [PATCH tip/core/rcu 02/21] mn10300: READ_ONCE() now implies smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:50 ` [PATCH tip/core/rcu 03/21] drivers/net/ethernet/qlogic/qed: Fix __qed_spq_block() ordering Paul E. McKenney
2017-12-01 19:50 ` [PATCH tip/core/rcu 04/21] fs/dcache: Use release-acquire for name/length update Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 05/21] percpu: READ_ONCE() now implies smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 06/21] rcu: Adjust read-side accessor comments for READ_ONCE() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 07/21] rtnetlink: Update now-misleading smp_read_barrier_depends() comment Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 08/21] seqlock: Remove now-redundant smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 09/21] uprobes: " Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 10/21] locking: Remove smp_read_barrier_depends() from queued_spin_lock_slowpath() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 11/21] tracepoint: Remove smp_read_barrier_depends() from comment Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 12/21] lib/assoc_array: Remove smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 13/21] mm/ksm: Remove now-redundant smp_read_barrier_depends() Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 14/21] netfilter: " Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 15/21] keyring: " Paul E. McKenney
2017-12-04 0:59 ` James Morris
2017-12-04 18:54 ` Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 16/21] drivers/infiniband: " Paul E. McKenney
2017-12-02 0:11 ` Jason Gunthorpe
2017-12-02 1:08 ` Paul E. McKenney
2017-12-05 15:08 ` Jason Gunthorpe
2017-12-05 20:06 ` Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 17/21] doc: De-emphasize smp_read_barrier_depends Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 18/21] genetlink: Remove smp_read_barrier_depends() from comment Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 19/21] netlink: " Paul E. McKenney
2017-12-01 19:51 ` [PATCH tip/core/rcu 20/21] checkpatch: Add warnings for {smp_,}read_barrier_depends() Paul E. McKenney
2017-12-01 20:14 ` Joe Perches
2017-12-01 21:44 ` Paul E. McKenney
2017-12-02 4:45 ` Joe Perches
2017-12-04 19:06 ` Paul E. McKenney
2017-12-04 19:12 ` Joe Perches
2017-12-01 19:51 ` [PATCH tip/core/rcu 21/21] drivers/vhost: Remove now-redundant read_barrier_depends() Paul E. McKenney
2017-12-05 18:31 ` Michael S. Tsirkin
2017-12-05 18:39 ` Peter Zijlstra
2017-12-05 18:57 ` Michael S. Tsirkin
2017-12-05 19:17 ` Peter Zijlstra
2017-12-05 19:24 ` Michael S. Tsirkin
2017-12-05 19:33 ` Paul E. McKenney
2017-12-05 19:51 ` Michael S. Tsirkin
2017-12-05 19:57 ` Peter Zijlstra
2017-12-05 20:28 ` Michael S. Tsirkin
2017-12-05 21:17 ` Peter Zijlstra
2017-12-05 21:42 ` Michael S. Tsirkin
2017-12-05 20:08 ` Paul E. McKenney
2017-12-05 21:24 ` Michael S. Tsirkin
2017-12-05 21:36 ` Paul E. McKenney
2017-12-05 21:43 ` Michael S. Tsirkin
2017-12-05 22:02 ` Paul E. McKenney
2017-12-05 22:09 ` Peter Zijlstra
2017-12-05 21:57 ` Peter Zijlstra
2017-12-05 22:09 ` Michael S. Tsirkin
2017-12-05 23:39 ` Paul E. McKenney
2017-12-05 19:55 ` Peter Zijlstra
2017-12-04 15:38 ` [PATCH tip/core/rcu 01/21] doc: READ_ONCE() now implies smp_barrier_depends() David Howells
2017-12-04 18:52 ` Paul E. McKenney
2017-12-04 21:54 ` Peter Zijlstra
2017-12-04 22:15 ` Paul E. McKenney [this message]
2017-12-04 22:39 ` David Howells
2017-12-04 22:57 ` Peter Zijlstra
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