Date: Wed, 21 Sep 2005 15:07:03 -0400 From: John Baldwin <jhb@FreeBSD.org> To: freebsd-amd64@freebsd.org Cc: amd64@freebsd.org Subject: Re: Patch to use fence instructions Message-ID: <200509211507.04755.jhb@FreeBSD.org> In-Reply-To: <433147C0.8030900@gneto.com> References: <200509201616.22475.jhb@FreeBSD.org> <433147C0.8030900@gneto.com>
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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 > performance? > > 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@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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