[Beowulf] crunch per kilowatt: GPU vs. CPU

[Bill Broadley]

Joe Landman wrote:
> Hi David
> 
> David Mathog wrote:
>> Although the folks now using CUDA are likely most interested in crunch
>> per unit time (time efficiency), perhaps some of you have measurements
>> and can comment on the energy efficiency of GPU vs. CPU computing?  That
>> is, which uses the fewest kilowatts per unit of computation.  My guess
> 
> Using theoretical rather than "actual" performance, unless you get the
> same code doing the same computation on both units:
> 
> 1 GPU ~ 960 GFLOP single precision, ~100 GFLOP double precision @ 160W

That sounds like the Nvidia flavor GPU, granted nvidia does seem to have a
larger lead over ATI for such use... at least till OpenCL gains more
popularity.  Nvidia's double precision rate is approximately 1/12th the single
their precision rate.  ATI's is around 1/5th, which results in around 240 GFlops.

So in both cases you get a pretty hefty jump if your application is single
precision friendly.

Of course such performance numbers are extremely application specific.  I've
seen performance increases published that are a good bit better (and worse)
than the GFlop numbers would indicate.  If you go to http://arxiv.org and type
CUDA in as a search word there are 10 ish papers that talk about various uses.

So basically it depends, either AMD, Intel, Nvidia, or ATI wins depending on
your application.  Of course there's other power efficient competition at
well, atom, via nano[1], sci cortex (mips), bluegene, and the latest
implmentation the PowerXCell 8i which is available in the QS22.

Assuming you have source code, and parallel friendly applications there's
quite a few options available.  Ideally future benchmarks would include power,
maybe add it as a requirement for future Spec benchmark submissions.

[1] http://www.theinquirer.net/inquirer/news/1137366/dell-via-nano-servers