Peer review of AMD64/FreeBSD article

[Brooks Davis]

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

-- 
Any statement of the form "X is the one, true Y" is FALSE.
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