From: Andi Kleen <ak@muc.de>
To: Andrew Morton <akpm@osdl.org>
Cc: Atsushi Nemoto <anemo@mba.ocn.ne.jp>,
clameter@engr.sgi.com, linux-kernel@vger.kernel.org,
ralf@linux-mips.org, johnstul@us.ibm.com,
Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH] simplify update_times (avoid jiffies/jiffies_64 aliasing problem)
Date: 4 Mar 2006 12:20:10 +0100
Date: Sat, 4 Mar 2006 12:20:10 +0100 [thread overview]
Message-ID: <20060304112010.GA94875@muc.de> (raw)
In-Reply-To: <20060304001834.0476e8e9.akpm@osdl.org>
> b) On 64-bit machines jiffies and jiffies_64 always have the same
> address (don't they?) Is the compiler really going to move a read of an
> absolute address ahead of a modification of the same address?
>
> <looks>
>
> The address of jiffies isn't known until link time, so yup, the risk
> is there.
Yes maybe it would be better to just use #define there.
jiffies_64 always was a bit too clever.
>
> c) jiffies is declared volatile. In practice, if I know my gcc, it's
> just not going to play these reordering games with a volatile.
>
> If that's true, and if some standard (presumably c99) says that it
> must be true then I don't think we need the patch.
The standards definition of volatile is unfortunately quite vague,
so at least from this side you cannot rely on much.
Also I assume Atsushi-san did the patch because he saw a real problem?
-Andi
next prev parent reply other threads:[~2006-03-04 11:20 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-03-02 14:02 [PATCH] simplify update_times (avoid jiffies/jiffies_64 aliasing problem) Atsushi Nemoto
2006-03-02 15:51 ` Atsushi Nemoto
2006-03-02 19:09 ` Christoph Lameter
2006-03-03 2:44 ` Atsushi Nemoto
2006-03-03 3:04 ` Andrew Morton
2006-03-03 3:20 ` Andi Kleen
2006-03-03 4:31 ` Atsushi Nemoto
2006-03-03 5:45 ` David S. Miller
2006-03-03 16:26 ` Atsushi Nemoto
2006-03-03 16:31 ` Atsushi Nemoto
2006-03-04 8:18 ` Andrew Morton
2006-03-04 11:20 ` Andi Kleen [this message]
2006-03-04 11:40 ` Andrew Morton
2006-03-04 5:21 ` Andi Kleen
2006-03-04 23:13 ` Paul Mackerras
2006-03-06 2:32 ` Atsushi Nemoto
2006-03-04 11:42 ` Paul Mackerras
2006-03-04 11:44 ` Andrew Morton
2006-03-04 12:33 ` Paul Mackerras
2006-03-04 16:43 ` Atsushi Nemoto
2006-03-03 20:17 ` john stultz
2006-03-03 21:15 ` Andrew Morton
2006-03-04 17:15 ` Atsushi Nemoto
2006-07-30 14:54 ` Atsushi Nemoto
2006-07-31 10:36 ` Martin Schwidefsky
2006-08-01 14:44 ` Atsushi Nemoto
2006-08-02 12:50 ` Martin Schwidefsky
2006-08-03 15:53 ` Atsushi Nemoto
2006-08-04 14:02 ` Martin Schwidefsky
2006-08-06 16:13 ` Atsushi Nemoto
2006-08-07 11:28 ` Martin Schwidefsky
2006-08-07 19:58 ` Andrew Morton
2006-08-08 8:11 ` Martin Schwidefsky
2006-08-09 15:07 ` Atsushi Nemoto
2006-03-03 18:13 ` john stultz
2006-03-04 2:34 ` Ralf Baechle
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