[gmx-users] GPU slower than I7

Roland Schulz roland at utk.edu
Fri Oct 22 00:35:48 CEST 2010

On Thu, Oct 21, 2010 at 5:53 PM, Renato Freitas <renatoffs at gmail.com> wrote:

> Thanks Roland. I will do a newer test using the fourier spacing equal
> to 0.11.

I'd also suggest to look at g_tune_pme and run with different rcoulomb,
fourier_spacing. As long as the ratio is the same you get the same accuracy.
And you should get better performance (especially on the GPU) for longer
cut-off and larger grid-spacing.

> However, about the performance of GPU versus CPU (mpi) let me
> try to explain it better:

>             NODE (s)                Real (s)                (%)
> Time:    6381.840                19210.349            33.2
>                            1h46:21
>                         (Mnbf/s)   (MFlops)     (ns/day)        (hour/ns)
> Performance:    0.000       0.001          27.077          0.886
>             NODE (s)         Real (s)                    (%)
> Time:    12621.257       12621.257               100.0
>                           3h30:21
>                      (Mnbf/s)      (GFlops)     (ns/day)        (hour/ns)
> Performance: 388.633      28.773        13.691         1.753

Yes. Sorry I didn't realize that NODE time and  Real time is different. Did
you run the GPU calculation on a desktop machine which was also doing other
things at the time. This might explain it. As far as I know for a dedicated
machine not running any other programs NODE and Real time should be the

Looking abobe we can see that the gromacs prints in the output that
> the simulation is faster when the GPU is used. But this is not the
> reality. The truth is that simulation time with MPI was 106 min faster
> thatn that with GPU. It seems correct to you? As I said before, I was
> expecting that GPU should take a lower time than the 6 core MPI.
 Well the exact time depends on a lot of factors. And you probably can speed
up both. But I would expect them to be both about similar fast.

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