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From: Christoph Lameter <cl@gentwo.org>
To: Tejun Heo <tj@kernel.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	David Howells <dhowells@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>,
	linux-kernel@vger.kernel.org,
	Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH RFC] percpu: add data dependency barrier in percpu accessors and operations
Date: Tue, 17 Jun 2014 10:56:10 -0500 (CDT)	[thread overview]
Message-ID: <alpine.DEB.2.11.1406171053230.20610@gentwo.org> (raw)
In-Reply-To: <20140617152752.GC31819@htj.dyndns.org>

On Tue, 17 Jun 2014, Tejun Heo wrote:


> * Add data dependency barrier to percpu accessors and write barrier to
>   the allocator with the comment that this will be replaced with
>   proper assignment macros and mark this change w/ -stable.
>
> * Later, introduce percpu pointer assignment macros and convert all
>   users and remove the wmb added above.

Uhhh no. The percpu stuff and the associated per cpu atomics are to be
used for stuff that is per cpu specific and runs at the fastest speed
doable at that level. Introducing implicit barriers is not that good an
idea.

The concurrency guarantees for the per cpu operations are related to being
interrupted or rescheduled but not for accesses from other processors.

Cpus maintain at least the appearance of operations being visible in
sequence for code running on the same processor. Therefore no barriers are
needed.


  reply	other threads:[~2014-06-17 15:56 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 [this message]
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
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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