lkml.org 
[lkml]   [2007]   [Aug]   [16]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
/
DateThu, 16 Aug 2007 16:00:05 +1000
FromPaul Mackerras <>
SubjectRe: [PATCH 0/24] make atomic_read() behave consistently across all architectures
Herbert Xu writes:

> It doesn't matter.  The memory pressure flag is an *advisory*
> flag.  If we get it wrong the worst that'll happen is that we'd
> waste some time doing work that'll be thrown away.

Ah, so it's the "racy but I don't care because it's only an
optimization" case.  That's fine.  Somehow I find it hard to believe
that all the racy uses of atomic_read in the kernel are like that,
though. :)

> In any case, this actually illustrates why the addition of
> volatile is completely pointless.  Even if this code was
> broken, which it definitely is not, having the volatile
> there wouldn't have helped at all.

Yes, adding volatile to racy code doesn't somehow make it race-free.
Neither does using atomic_t, despite what some seem to believe.

I have actually started going through all the uses of atomic_read in
the kernel.  So far out of the first 100 I have found none where we
have two atomic_reads of the same variable and the compiler could
usefully use the value from the first as the result of the second.
But there's still > 2500 to go...
Paul.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-08-16 08:27    [from the cache]
©2003-2008