perf events ring buffer memory barrier on powerpc

[Benjamin Herrenschmidt]

On Fri, 2013-11-01 at 18:30 +0200, Victor Kaplansky wrote:
> "David Laight" <David.Laight at aculab.com> wrote on 11/01/2013 06:25:29 PM:
> > gcc will do unexpected memory accesses for bit fields that are
> > adjacent to volatile data.
> > In particular it may generate 64bit sized (and aligned) RMW cycles
> > when accessing bit fields.
> > And yes, this has caused real problems.
> 
> Thanks, I am aware about this bug/feature in gcc.

AFAIK, this has been fixed in 4.8 and 4.7.3 ... 

Cheers,
Ben.

> -- Victor
> 
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