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• yafayez@yahoo.com 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 October 8, 2008 7:02 AM PDT Rate   #1 Re: Multithreading Big loop containing several loops inside 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 October 8, 2008 11:23 AM PDT Rate   #2 Reply To #1 Re: Multithreading Big loop containing several loops inside Quoting - jimdempseyatthecove 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 October 8, 2008 1:25 PM PDT Rate   #3 Reply To #2 Re: Multithreading Big loop containing several loops inside 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 October 8, 2008 2:26 PM PDT Rate   #4 Reply To #3 Re: Multithreading Big loop containing several loops inside Quoting - jimdempseyatthecove 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 October 8, 2008 5:46 PM PDT Rate   #5 Reply To #4 Re: Multithreading Big loop containing several loops inside 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 October 9, 2008 6:23 AM PDT Rate   #6 Reply To #4 Re: Multithreading Big loop containing several loops inside >>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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