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tangoman
Joined: 23 Aug 2007
Posts: 6
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 Posted: Thu Aug 23, 2007 2:33 am Post subject: How can I make -Mvect=sse and -mp work togehter? |
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Hi all,
I am trying to tune a numerical computing program with openmp on multi core AMD machine. I found the program with -mp option is much slower than the one without -mp when it runs with one thread. I post a simple test as following:
| Code: |
!$OMP PARALLEL
!$OMP DO PRIVATE(i,j,k)
do i=1,nx
do j=1,ny
do k=1,nz
tmp = c0*(a(k-4,j,i)+a(k+4,j,i))
& + c1*(a(k-3,j,i)+a(k+3,j,i))
& + c2*(a(k-2,j,i)+a(k+2,j,i))
& + c3*(a(k-1,j,i)+a(k+1,j,i))
& + c4*a(k,j,i)
b(k,j,i) = b(k,j,i)+c5*tmp
enddo
enddo
enddo
!$OMP END PARALLEL
I use –Minfo option to display compile-time optimization listings. It seems that the option -Mvect=sse conflits with -mp. The defference shows as following:
pgf90 -tp k8-64 -fastsse -Minfo -Mneginfo -c -o test.o test.f
my_test:
19, Generated 3 alternate loops for the inner loop
Generated vector sse code for inner loop
Generated 2 prefetch instructions for this loop
Generated vector sse code for inner loop
Generated 2 prefetch instructions for this loop
Generated vector sse code for inner loop
Generated 2 prefetch instructions for this loop
Generated vector sse code for inner loop
Generated 2 prefetch instructions for this loop
pgf90 -tp k8-64 -fastsse -mp -Minfo -Mneginfo -c -o test.o test.f
my_test:
15, Parallel region activated
17, Parallel loop activated; static block iteration allocation
19, Unrolled inner loop 8 times
Generated 2 prefetch instructions for this loop
29, Barrier
Parallel region terminated
How can I make them work togehter? Any suggestion is welcome.
Thanks!
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brentl
Joined: 20 Jul 2004
Posts: 107
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| Posted: Fri Aug 24, 2007 5:44 pm Post subject: |
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| You might need to declare tmp to be private. |
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tangoman
Joined: 23 Aug 2007
Posts: 6
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| Posted: Sun Aug 26, 2007 10:56 pm Post subject: |
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Yes, I made a mistake here. Thanks, brentl.
After I declared tmp as private, the optimization information is still a little different from the one without -mp flag.
15, Parallel region activated
17, Parallel loop activated; static block iteration allocation
19, Generated an alternate loop for the inner loop
Generated vector sse code for inner loop
Generated 2 prefetch instructions for this loop
Generated vector sse code for inner loop
Generated 2 prefetch instructions for this loop
29, Barrier
Parallel region terminated
Any suggestion? |
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brentl
Joined: 20 Jul 2004
Posts: 107
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| Posted: Thu Sep 13, 2007 11:02 am Post subject: |
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| Our altcode generator makes decisions based on a number of factors, being in a parallel region among them. That is why the differences. If you find it makes a big performance difference, you should let us know. Since the code vectorizes in both cases now, the code should be running fairly well. |
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tangoman
Joined: 23 Aug 2007
Posts: 6
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| Posted: Wed Sep 19, 2007 12:32 am Post subject: |
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| Thanks, these two version run almost at the same speed. |
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