Date: Mon, 26 Sep 2005 18:16:56 +0200 From: Martin Nilsson <martin@gneto.com> To: John Baldwin <jhb@FreeBSD.org> Cc: freebsd-amd64@freebsd.org Subject: Re: Patch to use fence instructions Message-ID: <43381EF8.2060308@gneto.com> In-Reply-To: <200509211507.04755.jhb@FreeBSD.org> References: <200509201616.22475.jhb@FreeBSD.org> <433147C0.8030900@gneto.com> <200509211507.04755.jhb@FreeBSD.org>
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John Baldwin wrote: > 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. I have tested the patch but I'm not able to see any difference with the mutex & threads tests in sysbench. On the other hand I'm not seeing any regressions either and everything seems to work OK. Can you suggest a better low-level test? /Martin
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