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SubjectRe: [PATCH 0/24] make atomic_read() behave consistently across all architectures


On Tue, 14 Aug 2007, Christoph Lameter wrote:

> On Thu, 9 Aug 2007, Chris Snook wrote:
>
> > This patchset makes the behavior of atomic_read uniform by removing the
> > volatile keyword from all atomic_t and atomic64_t definitions that currently
> > have it, and instead explicitly casts the variable as volatile in
> > atomic_read(). This leaves little room for creative optimization by the
> > compiler, and is in keeping with the principles behind "volatile considered
> > harmful".
>
> volatile is generally harmful even in atomic_read(). Barriers control
> visibility and AFAICT things are fine.

Frankly, I don't see the need for this series myself either. Personal
opinion (others may differ), but I consider "volatile" to be a sad /
unfortunate wart in C (numerous threads on this list and on the gcc
lists/bugzilla over the years stand testimony to this) and if we _can_
steer clear of it, then why not -- why use this ill-defined primitive
whose implementation has often differed over compiler versions and
platforms? Granted, barrier() _is_ heavy-handed in that it makes the
optimizer forget _everything_, but then somebody did post a forget()
macro on this thread itself ...

[ BTW, why do we want the compiler to not optimize atomic_read()'s in
the first place? Atomic ops guarantee atomicity, which has nothing
to do with "volatility" -- users that expect "volatility" from
atomic ops are the ones who must be fixed instead, IMHO. ]
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