graphicsmagick breaks torch matrix multiplication

[andreaskoepf]

Sounds strange first but I have this phenomena on three different Ubuntu 14.04.3 LTS machines and it is perfectly reproductible on my side.

As soon as I load the graphicsmagick module torch matrix multiplications of larger tensors end in an endlessloop with 100% CPU:

torch.ones(100, 100) * torch.ones(100, 100) -- no problem
require 'graphicsmagick'
torch.ones(10, 10) * torch.ones(10, 10) -- no problem
torch.ones(100, 100) * torch.ones(100, 100) -- never returns [!]

Smaller tensor-multiplications (e.g. 10x10) interestingly even work after the require 'graphicsmagick' statement.

Could somebody please check whether this effect only occurs on Ubuntu machines?

[soumith]

can verify that this:

• happens on Ubuntu 14.04
• does not happen in CentOS 6.6

[deltheil]

It looks like this problem is related to the use of omp_set_dynamic in old GraphicsMagick versions, e.g. on Ubuntu 14.04 / GraphicsMagick 1.3.18:

    /*
      Enable the dynamic adjustment of the number of threads up to the
      value set by omp_set_num_threads(), but only if there is more
      than one thread available.
    */
    if (getenv("OMP_DYNAMIC") == NULL)
      omp_set_dynamic(max_threads > 1);

(see magick/resource.c - this is part of initializations performed by InitializeMagick())

It has been reverted in the meanwhile:

    * magick/resource.c (InitializeMagickResources): Revert use of
    omp_set_dynamic() since it caused a severe performance regression
    when doing a -stepthreads benchmark or when the number of OpenMP
    threads is set via OMP_NUM_THREADS.

So the solution is to use a recent GraphicsMagick version, or turn off this mode via export OMP_DYNAMIC=FALSE.

[andreaskoepf]

I just tried to reproduce the problem on my Ubuntu 14.04 machine without setting OMP_DYNAMIC=FALSE but the 100x100 matrix multiplication executed now without problems.

The installed libGraphicsMagickWand.so.2.6.0 is from Dec 2013:

lrwxrwxrwx 1 root root 30 Dec 22  2013 /usr/lib/libGraphicsMagickWand.so -> libGraphicsMagickWand.so.2.6.0

[deltheil]

I reproduced the problem you reported on Ubuntu 14.04 with this exact version:

Dec 22  2013 /usr/lib/libGraphicsMagickWand.so.2.6.0

It corresponds to v1.3.18:

$ gm convert -version | head -n 1
GraphicsMagick 1.3.18 2013-03-10 Q8 http://www.GraphicsMagick.org/

And it was compiled with OpenMP support:

$ gm convert -version | grep -i openmp
  OpenMP                   yes (201107)
  CFLAGS   = -fopenmp

On this machine I verified that turning off the OMP_DYNAMIC mode solved the problem. On some other machines (Ubuntu 14.04, same GraphicsMagick version) I could not reproduce the problem for some reasons...