Tesla and Fermi cluster together...

Accelerated Computing CUDA CUDA Programming and Performance
1

I currently have a Tesla (S1070) cluster in production, and we’re going to expand it and thought of purchasing additional Fermis.
As far as I understand the current Tesla generation supports the IEEE 754-1985 spec for single precision. The new Fermi should support a newer version IEEE 754-2008.
What would happen if I have a mixed cluster of both Teslas and Fermis?
Will I get a different result for the same input data set (we do millions of single precision arithmetic operations) for Fermi and Tesla?

thanks
eyal

2

Yeah, you probably will. Fermi supports fused-multiply-add, GT200 doesn’t and only supports MAD (although it can emulate FMA at a major performance penalty). That means that Fermi has significantly improved precision versus GT200, but your results won’t line up unless you’re using the FMA intrinsics.

3

Thanks for the answer Tim.

So what is nVidia’s offical stand on how to handle this issue? What should I do with the “old” Tesla cluster?

I can’t take the performance hit just to keep the results the same and I do need the results to be the same.

What should I do? drop the Tesla cluster?

thanks

eyal

4

Well, question 1 is why you’re expecting single precision floating point operations to be the same across architectures. I wouldn’t necessarily trust them to be the same across Harpertown versus Nehalem, for instance, and things will certainly change again when going to Sandy Bridge which adds FMA support.

5

Not to mention that compiler upgrades (or even changing compiler options) will change the order of floating point operations on the same architecture, and give you different results as well.