Patch to use fence instructions
jhb at FreeBSD.org
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!
> > 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
> Sysbench is a benchmark specially made to determine lowlevel performance
> important for MySQL and be found here: http://sysbench.sourceforge.net/
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 FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" = http://www.FreeBSD.org
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