Patch to use fence instructions

[Martin Nilsson]

John Baldwin wrote:
> This patch changes the atomic operations and bus space barriers to use the x86 
> fence instructions.  Please test, thanks!
> 
> http://www.FreeBSD.org/~jhb/patches/amd64_fences.patch

What kind of performance improvements can we expect with this patch?
Is it worthwile to compare performance on dualcore Pentium D with 
sysbench before and after this patch? Does it affect threads & mutex 
performance?

Sysbench is a benchmark specially made to determine lowlevel performance 
important for MySQL and be found here: http://sysbench.sourceforge.net/

/Martin