[Beowulf] OpenMP on AMD dual core processors

Robert G. Brown rgb at phy.duke.edu
Fri Nov 21 11:44:38 EST 2008


On Fri, 21 Nov 2008, Nathan Moore wrote:

> 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.

Nathan,

This is simply a matter of practice.  Try coding with num_beer .ge. 10
for a few weeks, and then fall back to a lesser range.  I'd say .ge. 12
but it is so difficult to get vomit out of a keyboard... it might take
you a while to build up enough new smooth endoplasmic reticula to be
able to cope with the really high ranges.

For a special treat, try balancing out the beer fuzz with cocaine or
methamphetamines.  Much better than mere caffeine.  One can type so
FAST, you know.


:-)

    rgb

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

Robert G. Brown                            Phone(cell): 1-919-280-8443
Duke University Physics Dept, Box 90305
Durham, N.C. 27708-0305
Web: http://www.phy.duke.edu/~rgb
Book of Lilith Website: http://www.phy.duke.edu/~rgb/Lilith/Lilith.php
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