[Beowulf] Disappointing floating point performance for X5560 versus SPECmarks?

[Tom Elken]

> 
> Gerasimatos, Dimitrios V (343K) wrote:
> > According to SPECfp2006, the X5560 should blow the doors off of the
> E5430.
> > The X5560 scores 36 while the E5430 scores about 18.
> >
> >
> > However, our own benchmarking using nbench, unixbench, and a home-
> grown
> > utility (twobod) all show that any differences are attributed to
> clock speed.
> 
> I wouldn't use specfp**** ratios as a realistic guide for performance
> comparison.  As always, use your own code.

What Joe says has a lot of merit.

But that said, if your applications have advanced along with the capabilities of modern CPUs, SPECfp2006 is a lot better metric than SPECfp2000, which is a better metric than SPECfp95.  Each succeeding generation of SPEC CPU benchmark grows substantially in memory footprint and in the memory bandwidth performance required of a CPU/memory system.

I note that nbench and unixbench were last developed around 1996-1997 putting them in the same era of benchmarks as SPECfp95.

I see that the application components of SPECfp2006 for which X5560 blows the doors off E5430 (by 2x or more)  are: 410.bwaves (CFD), 433.milc (QCD), 450.soplex (Linear Programming), 459.GemsFDTD (Computational Electromagnetics), 470.lbm (CFD). These are CFP2006 applications which I remember as having the most memory bandwidth demand from my days on the CPU committee.

Since the Nehalem X5560 can do McaCalpin's STREAM (memory bandwidth, OpenMP 8-thread version) benchmark at about 3x the rate of Harpertown E5430, that explains a lot of the difference.

If you applications have a small memory footprint, or have great cache re-use, you probably don't need the newer generation of CPU.

-Tom


>  If your code shows 2x,
> great.  If not, then attribute the specfp**** to what they are
> (marketing numbers, with some grounding in reality, but not a firm
> comparison metric for dissimilar apps).
> 
> 
> 
> 
> 
> --
> Joseph Landman, Ph.D
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> Scalable Informatics Inc.
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