From: Arjan van de Ven <arjan@infradead.org>
To: Joseph Seigh <jseigh_02@xemaps.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: What does atomic_read actually do?
Date: Sat, 18 Dec 2004 19:34:27 +0100 [thread overview]
Message-ID: <1103394867.4127.18.camel@laptopd505.fenrus.org> (raw)
In-Reply-To: <opsi7o5nqfs29e3l@grunion>
On Sat, 2004-12-18 at 11:23 -0500, Joseph Seigh wrote:
> It doesn't do anything that would actually guarantee that the fetch from
> memory would be atomic as far as I can see, at least in the x86 version.
define atomic....
what linux atomics guarantee you is that you either "see" the old or the
new value if you use atomic_* as the sole accessor API, with the
footnote that this only holds if you don't forcefully misalign the
atomic_t.
if you want ordering guarantees on top... you need to use explicit
bariers for that (wmb/rmb and friends).
For the "no inbetween" rule, doing the read the way x86 does works on
x86, since x86 makes sure that on the write side, no intermediate
results become visible.
next prev parent reply other threads:[~2004-12-18 18:34 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-12-18 16:23 Joseph Seigh
2004-12-18 17:11 ` Paolo Ornati
2004-12-18 18:14 ` Joseph Seigh
2004-12-18 18:34 ` Arjan van de Ven [this message]
2004-12-18 19:20 ` Joseph Seigh
2004-12-18 19:39 ` Joe Korty
2004-12-18 19:54 ` Arjan van de Ven
2004-12-18 20:43 ` Joseph Seigh
2004-12-18 21:03 ` Brian Gerst
2004-12-19 22:21 ` Robert Love
2004-12-19 23:50 ` Joseph Seigh
2004-12-20 11:51 ` Arjan van de Ven
2004-12-20 12:52 ` Andrea Arcangeli
2004-12-20 20:51 ` Joseph Seigh
2004-12-18 20:47 ` Brian Gerst
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