ScaLAPACK Archives

[Scalapack] Process Grid Shape Trouble


Just for information which is the nonworking MPI? which is the working 
one?

Note:
* This MPI may be simply buggy
* BLACS may rely on specificty of MPI that are not explicitly in the 
standard but in most of MPI versions and so well

In any case, look like BLACS and this MPI are happy together. It would be 
good for us to know.

--j



On Thu, 8 Oct 2009, Jason Sadowski wrote:

Hi Jakub and Julien,

Thank you so much for your replies.? I've tried installing a new version of 
MPI and this seems to have resolved my issue.? I now get the correct
results independent of the shape of the process grid.

Thanks for the suggestions!

Jason

Jakub Kurzak wrote:
      Let throw in my $0.02.
      For the most part I agree with Julien.
      It happened to me before that a vendor MPI implementation was buggy in 
the shared memory part.
      Definitely trying a different MPI is a good idea.
      I saw the word "hyperthreading".
      Perhaps you meant "hypertransport"?
      I don't think hypertransport changes the memory consistency model, so 
it should not be an issue.
      I hope you're not using hyperthreading.
      There is no performance gain to be expected from that for ScaLAPACK.
      Jakub


      On Wed, Oct 7, 2009 at 10:47 AM, Julien Langou 
<julien.langou@Domain.Removed> wrote:

            This is indeed baffling (as you put it). There is not much reason 
for a ScaLAPACK code to perform correctly on a given
            machine and to perform incorrectly on another one. Moreover if 
you managed to get the incorrect installation to correctly
            work from time to time. A suggestion is to try a different MPI 
... I am not at all convinced that this will change the
            problem but I have no other suggestion.
            --j


            On Tue, 6 Oct 2009, Jason Sadowski wrote:

                  Hello All,

                  I am currently using ScaLapack to perform research at the 
University of Saskatchewan and have encountered some
                  peculiar problems.? I am using the PDSYEVD routine to
                  perform the diagonalization of a matrix however 
occasionally I get the wrong results.? I believe the problem may
                  be a memory issue, but I am unable to determine what
                  is causing it.? I am hoping somebody can give me an idea as 
to where this problem may be occurring.

                  The matrix I am trying to diagonalize is 3200x3200 and I am 
using a block size of 32x32.? I've noticed that the
                  eigenvalues returned by PDSYEVD are different
                  depending on the particular shape of the process grid I 
choose.? Inside my program I have the lines which
                  perform:

                  PRINT Matrix A
                  Diagonalize ( A, Z)
                  PRINT Matrix(Z)

                  Where A is the input matrix, and Z is the matrix of 
eigenvectors returned from PDSYEVD.? I want to perform this
                  calculation using 4 processors, so I can choose
                  process grids of 1x4, 2x2, or 4x1.? Here are the results of 
performing such calculations:

                  1) Matrix A is independent of the grid shape.? It is the 
same in all cases.
                  2) Matrix Z is INCORRECT for grid shapes of 2x2 and 1x4.
                  3) Process grid 4x1 gives the CORRECT values for MatrixZ.

                  As I have mentioned before, I believe this may be some kind 
of memory issue.? The reason I think this is because
                  I can perform the previous calculations on a
                  different machine (called vortex) with no errors.? 
Identical code ran on Vortex gives correct values of MatrixZ
                  for all grid shapes.? Only on this specific machine
                  (iglu) do the process grid problems arise.? To my knowledge 
the only difference between the machines is that
                  Vortex is a quad core machine with 8 GB of RAM, while
                  iglu is a dual core machine ( with hyperthreading enabled ) 
and 4 GB of RAM.?

                  First I should ask are there any known issues with 
ScaLapack's memory distribution scheme and hyperthreading
                  technology?? I realize this email is quite lengthy, but I
                  am completely baffled as to why this problem is occurring.? 
Any ideas or comments as to where I should be looking
                  would be greatly appreciated.

                  Sincerely,

                  Jason Sadowski
                  --
                  Jason Sadowski
                  jason.sadowski@Domain.Removed
                  Cell: 1-306-227-6066
                  "He who never made a mistake never made a discovery" - 
Samuel Smiles


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--
Jason Sadowski
jason.sadowski@Domain.Removed
Cell: 1-306-227-6066
"He who never made a mistake never made a discovery" - Samuel Smiles



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