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From: 42aftab_at_[hidden]
Date: 2007-10-25 06:42:12

Hi all,
       I am a research assistant (RA) at NUST Pakistan in High Performance
Scientific Computing Lab. I am working on the parallel
implementation of the Finitie Difference Time Domain (FDTD) method
using MPI. I am using the OpenMPI environment on a cluster of 4
SunFire v890 cluster connected through Myrinet. I am having problem
that when I run my code with let say 4 processes. Process 0 takes
about 3 times more time than other three processes, executing a for
loop which is the main cause of load imbalance in my code. I am
writing the code that is causing the problem. The code is run by
all the processes simultaneously and independently and I have timed
it independent of segments of code.

    start = gethrtime();
    for (m = 1; m < my_x ; m++){
      for (n = 1; n < size_y-1; n++) {
             Ez(m,n) = Ez(m,n) + cezh*((Hy(m,n) - Hy(m-1,n)) -
                                    (Hx(m,n) - Hx(m,n-1)));
     stop = gethrtime();
     time = (stop-start);

In my implementation I used 1-D array to realize 2-D arrays.I have used
the following macros for accesing the array elements.

  #define Hx(I,J) hx[(I)*(size_y) + (J)]
  #define Hy(I,J) hy[(I)*(size_y) + (J)]
  #define Ez(I,J) ez[(I)*(size_y) + (J)]

Can any one tell me what am I doing wrong here, or macros are creating the
problems or it can be related to any OS issue. I will be looking forward
for help because this problem has stopped my progress for the last two

regards aftab hussain

RA High Performance Scientific Computing Lab

NUST Institue of Information Technology

National University of Sciences and Technology Pakistan

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