From: Oliver Neukum <oliver@neukum.org>
To: "linux-os (Dick Johnson)" <linux-os@analogic.com>
Cc: "moreau francis" <francis_moreau2000@yahoo.fr>,
"Linux kernel" <linux-kernel@vger.kernel.org>
Subject: Re: question on memory barrier
Date: Wed, 24 Aug 2005 21:32:52 +0200 [thread overview]
Message-ID: <200508242132.52730.oliver@neukum.org> (raw)
In-Reply-To: <Pine.LNX.4.61.0508241347020.30497@chaos.analogic.com>
Am Mittwoch, 24. August 2005 20:22 schrieb linux-os (Dick Johnson):
> > sorry but I'm not sure to understand you...Do you mean that the first write
> > into reg_a pointer will be completed before the second write because they're
> > separated by a (;) ?
>
> Yes. The compiler must make sure that every effect of all previous
> code and all side-effects are complete at a "sequence-point". There
> are several sequence-points and the most obvious is a ";".
What the compiler may or may not generate is a little beside the point.
You have no guarantee that the CPU will execute these instructions in
the order given. If you need ordered writes use the appropriate barriers,
eg. wmb();
If this is PCI you also need to worry about the bridge caching. You
need to do dummy reads.
Regards
Oliver
next prev parent reply other threads:[~2005-08-24 19:33 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-08-24 12:43 moreau francis
2005-08-24 13:04 ` linux-os (Dick Johnson)
2005-08-24 17:31 ` moreau francis
2005-08-24 18:22 ` linux-os (Dick Johnson)
2005-08-24 19:32 ` Oliver Neukum [this message]
2005-08-24 19:47 ` linux-os (Dick Johnson)
2005-08-24 19:55 ` Oliver Neukum
2005-08-24 19:48 ` Andy Isaacson
2005-08-24 19:53 ` Jesse Barnes
2005-08-24 21:45 ` Alan Cox
2005-08-24 21:22 ` Jesse Barnes
2005-08-24 20:03 ` linux-os (Dick Johnson)
2005-08-24 20:21 ` Oliver Neukum
2005-08-25 2:25 ` David Schwartz
2005-08-25 8:49 ` Denis Vlasenko
2005-08-25 9:14 ` moreau francis
2005-08-25 10:07 ` Alan Cox
2005-08-25 14:54 ` Andy Isaacson
2005-08-26 7:21 ` moreau francis
2005-08-26 10:37 ` Maciej W. Rozycki
2005-08-25 10:32 ` Maciej W. Rozycki
2005-08-24 21:57 ` Alan Cox
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