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yafayez@yahoo.com
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60
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October 8, 2008 1:19 AM PDT
Multithreading Big loop containing several loops inside

Hi all,

Below please find my program. The program basically has a big loop and inside the big loop there are several loops that has to be executed in a certain way ( I put some remarks to show how it should be executed). Basically, every group of loops has to be exceuted fully " i.e all variables be updated before moving to the next loops". please let me know the best way and commands to use to ensure that the code is parallized only in the sequence showed in the code. Thanks,





do kk=1,temp     “ The Big Do LOOP”





     do i=nx1+1,nx2-2
     do j=ny1+2,ny2-2

     “stuff1”
enddo
enddo




     do i=nx1+2,nx2-2
     do j=ny1+1,ny2-2

     “stuff2”
enddo
enddo


/STUFF1 and STUFF2 can bw don in parellel but has to be completed before the below stuff



     
     es0=0.
     

do i=nx1,nx2
do j=ny1,ny2-1
do k=nz1,nz2-1
“stuff3”
enddo
enddo
enddo



do i=nx1,nx2-1
do j=ny1,ny2
do k=nz1,nz2-1
“stuff4”
enddo
enddo
enddo





do i=nx1,nx2-1
do j=ny1,ny2-1
do k=nz1,nz2
“stuff5”
enddo
enddo
enddo


/STUFF3 and STUFF4 and STUFF5 can be done in parellel but has to be completed before the below stuff





     call function1
     call function2
     
     

c
c update the E_field
c
c Main
c





     do j=ny1+1,ny2-1
do i=nx1,nx2-1
do k=nz1+1,nz2-1
STUFF6
enddo
enddo
enddo


     
     do j=ny1,ny2-1
do i=nx1+1,nx2-1
do k=nz1+1,nz2-1
STUFF7
enddo
enddo
enddo



     do j=ny1+1,ny2-1
do i=nx1+1,nx2-1
do k=nz1,nz2-1
STUFF8
enddo
enddo
enddo
/STUFF6 and STUFF7 and STUFF8 can be done in parellel but has to be completed before compiling the below stuff


      call function3
      call function4


     

enddo "ending the big do”

jimdempseyatthecove
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October 8, 2008 7:02 AM PDT
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#1


Is kk used inside your STUFF routines to select independent data sets?

If so, then can STUFF(...,kk) be executed in random order? (i.e. kk not dependent on kk-1)

Jim Dempsey


--------

Blog: The Parallel Void


www.quickthreadprogramming.com
yafayez@yahoo.com
Total Points:
60
Registered User
October 8, 2008 11:23 AM PDT
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#2 Reply to #1

Thanks first for your reply. no, the stuff at kk cannot be executed in random order because values of iterations from k-1 pass to k and so on "i.e. they are dependent". Please let me know your thoughts on these. Thanks again,

 

 


Is kk used inside your STUFF routines to select independent data sets?

If so, then can STUFF(...,kk) be executed in random order? (i.e. kk not dependent on kk-1)

Jim Dempsey

 
jimdempseyatthecove
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October 8, 2008 1:25 PM PDT
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#3 Reply to #2

You might start with something like the following:

!$omp parallel
!$omp do private(i,j)
do i=nx1+1,nx2-2
do j=ny1+2,ny2-2

     “stuff1”
enddo
enddo
!$omp end do nowait

 

!$omp do private(i,j)
do i=nx1+2,nx2-2
do j=ny1+1,ny2-2

     “stuff2”
enddo
enddo
!$omp end do nowait
!$omp end parallel

Note, depending on what is inside of stuff1 and stuff2 you may need to use different temporaries (or make subroutines out of stuff1 and stuff2 and passing i and j into the routines.

Also, if the computation overhead varies per iteration then experiment with adding the schedule clause.

Once you get the above working for stuff1 and stuff2 apply what you learned to the remaining stuff sections.

Jim Dempsey

 


--------

Blog: The Parallel Void


www.quickthreadprogramming.com
yafayez@yahoo.com
Total Points:
60
Registered User
October 8, 2008 2:26 PM PDT
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#4 Reply to #3

Hi,

 

I added the commands and i see that all processors are working but the program is much slower. How can i detect bootlenick. Thanks, is there a phone number i can call you at to discuss it more. Thanks again,

 

Yasser

You might start with something like the following:

!$omp parallel
!$omp do private(i,j)
do i=nx1+1,nx2-2
do j=ny1+2,ny2-2

     “stuff1”
enddo
enddo
!$omp end do nowait

 

!$omp do private(i,j)
do i=nx1+2,nx2-2
do j=ny1+1,ny2-2

     “stuff2”
enddo
enddo
!$omp end do nowait
!$omp end parallel

Note, depending on what is inside of stuff1 and stuff2 you may need to use different temporaries (or make subroutines out of stuff1 and stuff2 and passing i and j into the routines.

Also, if the computation overhead varies per iteration then experiment with adding the schedule clause.

Once you get the above working for stuff1 and stuff2 apply what you learned to the remaining stuff sections.

Jim Dempsey

 

 
jimdempseyatthecove
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October 8, 2008 5:46 PM PDT
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#5 Reply to #4


email me at

  j i m _ d e m p s e y @ a m e r i t e c h . n e t

(remove the spaces)

Jim Dempsey


--------

Blog: The Parallel Void


www.quickthreadprogramming.com
jimdempseyatthecove
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October 9, 2008 6:23 AM PDT
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#6 Reply to #4


>>I added the commands and i see that all processors are working but the program is much slower. How can i detect bootlenick.

This is symptomatic of the inner OpenMP do loop running serially. Place the "!$OMP DO ..." (or "C$OMP DO ..." at the left margine.

Should this not improve matters then try

!$omp parallel do private(i,j)
do i=nx1+1,nx2-2
do j=ny1+2,ny2-2

     “stuff1”
enddo
enddo
!$omp end parallel do

 

!$omp parallel do private(i,j)
do i=nx1+2,nx2-2
do j=ny1+1,ny2-2

     “stuff2”
enddo
enddo
!$omp end parallel do

Note, the above is not inside an !$OMP PARALLEL region

The purpose of coding the first way was to permit the threads finishing the STUFF1 loop first to begin processing the STUFF2 loop prior to the remaining threads working on STUFF1 loop finishing.

If this too does not improve the performance then the code in STUFF1 and STUFF2 are likely memory copy statements as opposed to computational statements.

Jim Dempsey


--------

Blog: The Parallel Void


www.quickthreadprogramming.com


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