Date: Fri, 12 Mar 2004 15:33:20 -0500 From: Jem Matzan <valour@thejemreport.com> To: freebsd-amd64@freebsd.org Subject: Re: Peer review of AMD64/FreeBSD article Message-ID: <40521E90.8090102@thejemreport.com> In-Reply-To: <20040312195958.GA32345@Odin.AC.HMC.Edu> References: <200403121301.i2CD1oQC076505@lurza.secnetix.de> <4051B7D3.8020404@thejemreport.com> <20040312174736.GD7661@Odin.AC.HMC.Edu> <4052130E.9060601@thejemreport.com> <20040312195958.GA32345@Odin.AC.HMC.Edu>
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Brooks Davis wrote: >On Fri, Mar 12, 2004 at 02:44:14PM -0500, Jem Matzan wrote: > > >>Brooks Davis wrote: >> >> >> >>>On Fri, Mar 12, 2004 at 08:14:59AM -0500, Jem Matzan wrote: >>> >>> >>> >>> >>>>Hyper-Threading seemed to help with processes that didn't require a >>>>heavy CPU load. The OpenSSL tests show it being markedly faster in the >>>>smaller algorithms, but lagging way behind the 64-bit Athlon64 when the >>>>serious number crunching comes into play. Intel's press kit shows HT >>>>(and SSE3) giving an advantage when multitasking with four desktop >>>>programs in Windows XP. It's just too hard to show that reliably though. >>>>There's a lot of anecdotal evidence to suggest that AMD64 is faster on >>>>the desktop (in X) in 64-bit mode than the Prescott is in 32-bit, but >>>>I'm having trouble proving it. >>>> >>>> >>>> >>>> >>>I think it would be a mistake to assume the HT is what accounts for >>>the performance difference. There are so many other architectural >>>differences it's hard to see how you could isolate the effects of >>>HT. My suspicition is that better performance on small >>>algorithms is due to them being more or less memory bound (and thus >>>similar to the pure synthetic benchmarks). >>> >>> >>> >>By comparing the Pentium4 to the Athlon64 in i386 mode, you can better >>see the advantage of HT Technology. This is especially evident in the >>OpenSSL tests. >> >> > >I strongly disagree. All you can see is that they differ. The >architectural differences between P4 CPUs and current generation amd64 >CPUs are a whole lot more then HT. You've got a different memory memory >system, vastly different pipeline lengths, etc. For that matter, >on paper at least, I wouldn't expect HT to help much if any in this >situation since you're not trying to do two things at once. > >-- Brooks > > > I'm pretty sure I did mention that, but I'll go over the article to make sure it's clear that the reason why there is a performance difference could be due to a number of factors (which are listed here). -Jem
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