Patch to use fence instructions

John Baldwin jhb at
Wed Sep 21 12:16:40 PDT 2005

On Wednesday 21 September 2005 07:45 am, Martin Nilsson wrote:
> John Baldwin wrote:
> > This patch changes the atomic operations and bus space barriers to use
> > the x86 fence instructions.  Please test, thanks!
> >
> >
> 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:

I'm not sure what improvements it would provide (I don't have any amd64 
hardware to test on anyway).  I believe that in some microbenchmarks bde@ 
found that just using lfence or sfence was only about half the cost of using 
the 'lock' prefix.  Thus, things like atomic_store_rel (used in mutexes) 
might perform better.

John Baldwin <jhb at>  <><
"Power Users Use the Power to Serve"  =

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