[gmx-developers] gromacs 5.1rc1 OpenCL problem with Parrinello-Rahman

[Mark Abraham]

Hi,

Thanks. If a difference of that magnitude can be seen, then it should also
show up when running the regressiontests (e.g. cmake
-DREGRESSIONTEST_DOWNLOAD=on and then make check) as a failure
of complex/nbnxn-ljpme-LB (which is the only P-R test that can run on the
GPU). If other tests fail, then the problem is actually more widespread.

It may be that there is some issue with some part of the Mac+clang+OpenCL
stack - we didn't target it during development, and at the last minute when
Erik was unexpectedly able to get it to compile. I don't know if he got
tests to pass. Erik?

Mark

On Wed, Jul 15, 2015 at 5:22 PM Carlo Camilloni <carlo.camilloni at gmail.com>
wrote:

>
> Dear Mark and Szilard,
>
> thanks for your answer. I filed a bug in redmine but in the meantime I was
> running more tests and I am a bit scared by what I found:
>
> what I have done is the following I have performed a single step run with
> gmx51-rc1 compiled with cuda, again clang and so on
> and compared the forces on the first step with -nb cpu or not (I am using
> -pforce 1), the forces are identical:
>
> ie.:
>
> cuda-gpu
>
> step 0  atom      1  x    3.940    5.612    2.226  force  1.90839e+03
> step 0  atom      2  x    3.852    5.659    2.211  force  4.24845e+02
> step 0  atom      3  x    3.979    5.665    2.303  force  6.89472e+02
> step 0  atom      4  x    3.992    5.610    2.139  force  7.42053e+02
>
>
> cpu:
>
> step 0  atom      1  x    3.940    5.612    2.226  force  1.90839e+03
> step 0  atom      2  x    3.852    5.659    2.211  force  4.24845e+02
> step 0  atom      3  x    3.979    5.665    2.303  force  6.89472e+02
> step 0  atom      4  x    3.992    5.610    2.139  force  7.42053e+02
>
> if I do the same test on the version compiled with OpenCL
>
> cpu:
>
> (the former are done on my macbook pro avx2_256  this latter on a MacPro
> avx_256, this should
> explain the small differences in the forces)
>
> step 0  atom      1  x    3.940    5.612    2.226  force  1.90838e+03
> step 0  atom      2  x    3.852    5.659    2.211  force  4.24848e+02
> step 0  atom      3  x    3.979    5.665    2.303  force  6.89470e+02
> step 0  atom      4  x    3.992    5.610    2.139  force  7.42043e+02
>
> opencl-gpu:
> step 0  atom      1  x    3.940    5.612    2.226  force  1.48597e+03
> step 0  atom      2  x    3.852    5.659    2.211  force  6.26942e+02
> step 0  atom      3  x    3.979    5.665    2.303  force  8.44032e+02
> step 0  atom      4  x    3.992    5.610    2.139  force  7.92786e+02
>
> I am afraid there is something wrong  in OpenCL kernels.
>
> I am using the topol-nvt-nogen.tpr I have uploaded on redmine.
>
> Best,
> Carlo
>
>
>
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