[lkml]   [2007]   [Aug]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 0/24] make atomic_read() behave consistently across all architectures

On Fri, 17 Aug 2007, Segher Boessenkool wrote:

> > > atomic_dec() already has volatile behavior everywhere, so this is
> > > semantically
> > > okay, but this code (and any like it) should be calling cpu_relax() each
> > > iteration through the loop, unless there's a compelling reason not to.
> > > I'll
> > > allow that for some hardware drivers (possibly this one) such a compelling
> > > reason may exist, but hardware-independent core subsystems probably have
> > > no
> > > excuse.
> >
> > No it does not have any volatile semantics. atomic_dec() can be reordered
> > at will by the compiler within the current basic unit if you do not add a
> > barrier.
> "volatile" has nothing to do with reordering.

If you're talking of "volatile" the type-qualifier keyword, then (and sub-thread below it) shows

> 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.

I don't think an atomic_dec() implemented as an inline "asm volatile"
or one that uses a "forget" macro would have the same re-ordering
guarantees as an atomic_dec() that uses a volatile access cast.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2007-08-17 20:57    [W:0.264 / U:20.140 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site