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Bo_Q_
Beginner
37 Views

Xeon w3680 runs slower than i5-3320M

Hi,

I have strange problem where the same program runs faster on a i5-3320M than an Xeon w3680. The main part of the code is FFT. Could anyone shine some light on me? Thanks!

 

 

 

 

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2 Replies
TimP
Black Belt
37 Views

Presumably, you're using MKL which gains a big advantage from AVX on the newer CPU. 

Maybe you didn't check out settings which might optimize thread placement across the 4 cache channels of the Westmere CPU, e.g. KMP_AFFINITY="proclist=[1,3-5],verbose,explicit" with MKL_NUM_THREADS=4 and HyperThreading disabled (just guessing, according to a typical BIOS numbering of the cores).  I suppose, with HT enabled, it might be proclist=[3,7,9,11] or some such.  HT wasn't designed for simplicity, nor was there a consistent pattern in early BIOS for it.

If you did so, some specifics of your results might help you get more intelligent responses.  The quirky cache setup of the 6-core Westmere probably contributes to limited popularity (and the fact that I have one left to me as a retirement gift).

Also, you should check the MKL docs for any recommendations such as 32-byte data alignment (at least as important on older core-I7 CPUs as the newer one).

Gennady_F_Intel
Moderator
37 Views

What is problem size? and

What is performance difference you are talking about?

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