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From: 42aftab_at_[hidden]
Date: 2007-10-26 05:10:44


Thanks,

 The array bounds are the same on all the nodes and also the compute nodes
are identical i.e. SunFire V890 nodes. And I have also changed the root
process to be on different nodes, but the problem remains the same. I
still dont understand the problem very well and my progress is in stand
still situation.

regards aftab hussain

Hi,

    Please ensure if following things are correct
1) The array bounds are equal. Means "my_x" and "size_y" has the same
value on all nodes.
2) Nodes are homogenous. To check that, you could decide root to be some
different node and run the program

-Neeraj

On Fri, October 26, 2007 10:13 am, 42aftab_at_[hidden] wrote:
> Thanks for your reply,
>
>
> I used MPI_Wtime for my application but even then process 0 took longer
> time executing the mentioned code segment. I might be worng, but what I see
> is process 0 takes more time to access the array elements than other
> processes. Now I dont see what to do because the mentioned code segment is
> creating a bottleneck for the timing of my application.
>
> Can any one suggest somthing in this regard. I will be very thankful
>
>
> regards
>
> Aftab Hussain
>
>
>
> On Thu, October 25, 2007 9:38 pm, jody wrote:
>
>> HI
>> I'm not sure if that is a problem,
>> but in MPI applications you shoud use MPI_WTime() for time-measurements
>>
>> Jody
>>
>>
>>
>> On 10/25/07, 42aftab_at_[hidden] <42aftab_at_[hidden]> wrote:
>>
>>
>>> 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 weeks
>>>
>>> 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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