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Date:	Tue, 11 Sep 2007 04:27:22 +0200
From:	Segher Boessenkool <>
To:	Christoph Lameter <>
Cc:	Paul Mackerras <>,,, Stefan Richter <>,
	Satyam Sharma <>,
	Linux Kernel Mailing List <>,
	David Miller <>,
	"Paul E. McKenney" <>,
	Ilpo Järvinen <>,,,,
	Netdev <>,,,
	Andrew Morton <>,,, Chris Snook <>,
	Herbert Xu <>,
	Linus Torvalds <>,,
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

>> "volatile" has nothing to do with reordering.  atomic_dec() writes
>> to memory, so it _does_ have "volatile semantics", implicitly, as
>> long as the compiler cannot optimise the atomic variable away
>> completely -- any store counts as a side effect.
> Stores can be reordered. Only x86 has (mostly) implicit write ordering.
> So no atomic_dec has no volatile semantics

Read again: I said the C "volatile" construct has nothing to do
with CPU memory access reordering.

> and may be reordered on a variety
> of processors. Writes to memory may not follow code order on several
> processors.

The _compiler_ isn't allowed to reorder things here.  Yes, of course
you do need stronger barriers for many purposes, volatile isn't all
that useful you know.


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