MATLAB: GpuArray slower on newer graphics card in double precision

gpuarrayParallel Computing Toolboxspeed comparison

I have been making the following speed test in R2015a on two different computers running two different graphics cards,
>> A=gpuArray(rand(5e3));
>> T=gputimeit(@()A*A)
The first computer is an older model (Dell Precision T7500) running an older graphics card (GTX 580). The second, newer computer (Dell Precision Tower 7910) is running a newer graphics card (Titan X).
Oddly, I find that the older configuration outperforms the newer by about 20%. The GTX 580 gives T=1.1178 seconds, whereas the Titan X gives T=1.3097 seconds. When I redo the test in single precision,
    >> A=gpuArray(rand(5e3,'single'));
    >> T=gputimeit(@()A*A)
the results are more in line with my expectations. The GTX 580 gives T=0.2121 seconds, whereas the Titan X gives T=0.0491 seconds.
I'm wondering what could account for this difference. One thing that might be worth mentioning is that the Titan X is not using a fully updated driver. At the time of this writing, there is some bug in its newest driver release, making it unusable, and I am instead using driver version 353.62. Could this be the reason? If not, any other ideas?

Best Answer

The Titan X is a terrible card to use for double precision GPGPU as it was designed as a cheaper alternative to other Titans with a focus on single precision (gaming). You will see that the GFLOPS for double precision is about 1/32 that of single precision on the Maxwell chips. Compare that with the Fermi architecture used on the GTX 580 which has 1/5 the GFLOPS for double precision compared with its single precision. If you intended to use this for double precision I would highly recommend using the Titan Z (or Black) which uses the Kepler architecture. Therefore if you have a Titan Black, this would not be rolling back at all, but rather using a card which considered double precision as being important.
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