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[Tom Elken]

> > > On Behalf Of Dmitry Zaletnev
>>> What would be the difference in overall performance
> (I suppose, due to the memory access time) between Q9650/ 8 GB DDR2-
> 800
> > > and i7 920/ 6 GB DDR3-1866.
> > you probably mean "DDR3-1066".
> Tom, thank you for your answer, here I mean 1866 MHz, OCZ3P1866C7LV6GK
> kits. I expect their availability must grow up till the end of the
> winter when I'm going to finalize the construction of my home Beowulf.

OK. I didn't know that desktop memory was so much faster than the top-end server memory of DDR3-1333 we have in our cluster.  BTW, we've had a lot of dimm and/or dimm slot issues at this speed, so I would hesitate using the "bleeding edge" memory speed if reliability is important to you.

For the rest of the Beowulf list, I had meant to CC you on my response to Dmitry.  Here it is the rest of my response:

"
Concerning overall CFD performance, I would go for the i7 920.

For CFD performance data, one good resource are the FLUENT benchmark pages:
http://www.fluent.com/software/fluent/fl6bench/fl6bench_6.4.x/index.htm
click on one of the 6 test datasets there and get tables of benchmark performance.  For example the Aricraft_2m model (with  at:
http://www.fluent.com/software/fluent/fl6bench/fl6bench_6.4.x/problems/aircraft_2m.htm
The Nehalem (same architecture as i7 920) generation:
INTEL WHITEBOX (INTEL_X5570_NHM4,2930,RHEL5)*
FLUENT rating  at 8 cores: = 784.9

The Harpertown generation (same architecture as Q9650, I think)
INTEL WHITEBOX (INTEL_X5482_HTN4,3200,RHEL5)
FLUENT rating  at 8 cores: = 307.6

* To help decode these brief descriptions of processors, systems & interconnects, you can often find more details at this page:  http://www.fluent.com/software/fluent/fl6bench/new.htm


THe FLUENT rating is a "bigger is better" metric relating to the number of jobs you can run in 24 hours, IIRC.

So with the newer generation, on these FLUENT benchmarks anyway, you get approximately 2x the performance.

> By the way, are local variables of
> methods/functions stored in L2 cache? 

There are 3 levels of cache in the i7, 2 levels in the Q9650.
All your problems are likely to use all levels of cache.  You are right that data you tend to reuse frequently will tend to live in the lower cache levels longer, but there are no hard and fast rules.

Best of luck,
Tom
"

> I'm slightly confused: the test results from the Corsair site tell
> about significant difference in performance between i7 with 1333 MHz
> memory and 1866 MHz memory, from other side Tom's hardware forum tells
> that the only parameter that matters is the latency and there's no
> difference between a low-latency 1333 MHz memory and 1600 MHz memory.
> But I'm afraid that chosing 1333 MHz memory now will eliminate the
> sense of future upgrade to Xeon (motherboard supports it) or Fermi-in-
> SLI.
> 
> Best regards,
> Dmitry