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From: Christoph Lameter <cl@gentwo.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>,
	Rusty Russell <rusty@rustcorp.com.au>,
	Andrew Morton <akpm@linux-foundation.org>,
	Tejun Heo <tj@kernel.org>, David Howells <dhowells@redhat.com>,
	linux-kernel@vger.kernel.org, Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH RFC] percpu: add data dependency barrier in percpu accessors and operations
Date: Tue, 17 Jun 2014 13:47:01 -0500 (CDT)	[thread overview]
Message-ID: <alpine.DEB.2.11.1406171345240.21931@gentwo.org> (raw)
In-Reply-To: <CA+55aFxHr8JXwDR-4g4z1mkXvZRtY=OosYcUMPZRD2upfooS1w@mail.gmail.com>


On Tue, 17 Jun 2014, Linus Torvalds wrote:

> On Jun 17, 2014 6:28 AM, "Christoph Lameter" <cl@gentwo.org> wrote:
> >
> > Even alpha maintains the illusion of changes becoming visible in the
> > proper order for the currently executing thread. No barriers are needed.
>
> No Christoph, alpha really doesn't. Barriers needed.

Everythig breaks if a single hardware execution thread can no longer
observe a consistent view of the world of the data it modifies.

We are not talking about synchronization here between multiple hardware
threads. This is simply code running on a single hardware thread and all
architectures maintain the uniprocessor illusion there.



  parent reply	other threads:[~2014-06-17 18:47 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-06-12 13:56 [PATCH RFC] percpu: add data dependency barrier in percpu accessors and operations Tejun Heo
2014-06-12 15:34 ` Paul E. McKenney
2014-06-12 15:52   ` Tejun Heo
2014-06-17 14:41     ` Paul E. McKenney
2014-06-17 15:27       ` Tejun Heo
2014-06-17 15:56         ` Christoph Lameter
2014-06-17 16:00           ` Tejun Heo
2014-06-17 16:05             ` Tejun Heo
2014-06-17 16:28               ` Christoph Lameter
     [not found]                 ` <CA+55aFxHr8JXwDR-4g4z1mkXvZRtY=OosYcUMPZRD2upfooS1w@mail.gmail.com>
2014-06-17 18:47                   ` Christoph Lameter [this message]
2014-06-17 18:55                     ` Paul E. McKenney
2014-06-17 19:39                       ` Christoph Lameter
2014-06-17 19:47                         ` Tejun Heo
2014-06-17 19:56                         ` Paul E. McKenney
2014-06-19 20:39                           ` Christoph Lameter
2014-06-17 16:57         ` Paul E. McKenney
2014-06-17 18:56           ` Tejun Heo
2014-06-17 19:42             ` Christoph Lameter
2014-06-17 20:44               ` Tejun Heo
2014-07-09  0:55         ` Rusty Russell
2014-07-14 11:39           ` Paul E. McKenney
2014-07-14 15:22             ` Christoph Lameter
2014-07-15 10:11               ` Paul E. McKenney
2014-07-15 14:06                 ` Christoph Lameter
2014-07-15 14:32                   ` Paul E. McKenney
2014-07-15 15:06                     ` Christoph Lameter
2014-07-15 15:41                       ` Linus Torvalds
2014-07-15 16:12                         ` Christoph Lameter
     [not found]                           ` <CA+55aFxU166V5-vH4vmK9OBdTZKyede=71RjjbOVSN9Qh+Se+A@mail.gmail.com>
2014-07-15 17:45                             ` Paul E. McKenney
2014-07-15 17:41                       ` Paul E. McKenney
2014-07-16 14:40                         ` Christoph Lameter
2014-07-15 11:50             ` Rusty Russell
2014-06-17 19:27 ` Christoph Lameter
2014-06-17 19:40   ` Paul E. McKenney
2014-06-19 20:42     ` Christoph Lameter
2014-06-19 20:46       ` Tejun Heo
2014-06-19 21:11         ` Christoph Lameter
2014-06-19 21:15           ` Tejun Heo
2014-06-20 15:23             ` Christoph Lameter
2014-06-20 15:52               ` Tejun Heo
2014-06-19 20:51       ` Paul E. McKenney
2014-06-20 15:29         ` Christoph Lameter
2014-06-20 15:50           ` Paul E. McKenney

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