[Beowulf] OpenMP on AMD dual core processors

Nathan Moore ntmoore at gmail.com
Fri Nov 21 07:45:36 PST 2008


Hi Joe,

I found the article you wrote for Linux Journal right about the time you
emailed last night - thanks for the reference and the suggestions!  I find
that 1 beer and coding is ok, but num_beer .ge. 2 makes me too poetic and
insufficiently detail oriented.  Debugging the next morning is never fun.

On Fri, Nov 21, 2008 at 9:23 AM, Joe Landman <
landman at scalableinformatics.com> wrote:

> Geoff Jacobs wrote:
>
>  If this were done with MPI, one would have to be careful of the
>> boundaries on the matrix as it's partitioned for computation. OpenMP is
>> intelligent enough to hold off computation on the tiles south and east
>> of the first until the first is done, and so forth?
>>
>
> No... I didn't address the interior vs exterior.  I have a nice worked
> example where I convert this sort of code into an exterior, a skin, and the
> communication for an MPI and OpenMP version.  Scales pretty well. You are
> right, I should have fixed that as well.
>
>
>>  ! now all you need is a "linear scan" to find positive elements in
>>> ! dv.  You can approach these as sum reductions, and do them in
>>> ! parallel
>>> do i=1,Nx
>>>  sum=0.0
>>>  do j=1,Ny
>>>  sum = sum + dabs(dv(i,j) .gt. 0.0) * dv(i,j)
>>>  end do
>>>  if (sum .gt. 0.0) converged = 0
>>> end do
>>>
>>> The basic idea is to replace the inner loop conditionals and remove as
>>> many of the shared variables as possible.
>>>
>>
>> Yup, keep things pipelined.
>>
>
> That was the idea, though I didn't compile/test the code to be sure it
> would work.  That and I usually try to avoid real coding when I am tired at
> night.  Coding and beer don't mix (for me).
>
>
>
>
> --
> Joseph Landman, Ph.D
> Founder and CEO
> Scalable Informatics LLC,
> email: landman at scalableinformatics.com
> web  : http://www.scalableinformatics.com
>       http://jackrabbit.scalableinformatics.com
> phone: +1 734 786 8423 x121
> fax  : +1 866 888 3112
> cell : +1 734 612 4615
>



-- 
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Nathan Moore
Assistant Professor, Physics
Winona State University
AIM: nmoorewsu
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