Loop nest parallelized with !$omp parallel do collapse() does not run

Loop nest parallelized with !$omp parallel do collapse() does not run

Ritratto di styc
styc
Gio, 18/10/2012 - 00:10

Compile the following test program ifort 13.0.

program test integer i, j double precision, allocatable :: a(:, :) allocate(a(5, 6)) !$omp parallel do collapse(2) private(i, j) do j = 1, 6 do i = 1, 5 a(i, j) = i * 10 + j end do end do !$omp end parallel do print *, a !$omp parallel do collapse(2) private(i, j) do i = 1, size(a, 1) do j = 1, size(a, 2) !$omp critical print *, a(i, j) !$omp end critical end do end do !$omp end parallel do end program

When the program is run, no output is produced from the second loop nest.

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Ritratto di Kevin Davis (Intel)
Kevin Davis (Intel)
Gio, 18/10/2012 - 02:48

Thank you for the nice reproducer. Unclear whether the root cause is tied to collapse or size() in the second loop nest. The second loop nest runs w/o collapse but w/size, or w/o size but w/collapse. I reported to Development (internal tracing id below) for further analysis and will update once I learn more.

(Internal tracking id: DPD200237575)

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Ritratto di styc
styc
Gio, 18/10/2012 - 13:53

Quote:

Kevin Davis (Intel) wrote:

Thank you for the nice reproducer. Unclear whether the root cause is tied to collapse or size() in the second loop nest. The second loop nest runs w/o collapse but w/size, or w/o size but w/collapse. I reported to Development (internal tracing id below) for further analysis and will update once I learn more.

(Internal tracking id: DPD200237575)

This is another troubling case involving the collapse clause.

program test

    integer s(3), e(3), i, j, k, l

    s = 1
    e = 64

    !$omp parallel do collapse(2) private(i, j, k, l)
    do l = 1, 2
        do j = s(2), e(2)
            do k = s(3), e(3)
                do i = s(1), e(1)
                    !$omp critical
                    print *, i, j, k, l
                    !$omp end critical
                end do
            end do
        end do
    end do

end program

The program outputs only 8192 lines instead of the expected 524,288. Notice that j only ever takes two values (1 and 2).

I need an immediate workaround for this problem. Please confirm if using scalar variables for loop bounds always works.

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Ritratto di TimP (Intel)
TimP (Intel)
Gio, 18/10/2012 - 14:09

I'd certainly hesitate to say "always" but I've had better luck with getting fixes for collapse with scalar loop bounds known at compile time, and my broken cases involve variable sizes.

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Ritratto di Kevin Davis (Intel)
Kevin Davis (Intel)
Ven, 19/10/2012 - 02:30

Unfortunately I can only produce correct results w/o collapse. I reported this case separately and requested advice for any other work around.

(Internal tracking id: DPD200237626)

(Resolution Update on 02/08/2013): This defect is fixed in the Intel Fortran Composer XE 2013 Update 2 (2013.2.146 - Linux) 

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Ritratto di Kevin Davis (Intel)
Kevin Davis (Intel)
Gio, 01/11/2012 - 11:17

I thought the second case was fixed in our latest XE 2013 Update 1, but that appears not to be true. Still awaiting resolution of both cases.

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Ritratto di jimdempseyatthecove
jimdempseyatthecove
Ven, 02/11/2012 - 07:46

For a work around, remove the collapse, swap the "do l" and "do j" lines.
This will change the sequence.
An alternative work around:
s = 1
e = 64
!$omp parallel private(i, j, k, l)
do l = 1, 2
!$omp do
do j = s(2), e(2)
do k = s(3), e(3)
do i = s(1), e(1)
!$omp critical
print *, i, j, k, l
!$omp end critical
end do
end do
end do
!$omp barrier
end do

Jim Dempsey

Blog: The Parallel Void

www.quickthreadprogramming.com
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Ritratto di jimdempseyatthecove
jimdempseyatthecove
Sab, 03/11/2012 - 05:28

(forum double posted message removed)

Blog: The Parallel Void

www.quickthreadprogramming.com
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Ritratto di Kevin Davis (Intel)
Kevin Davis (Intel)
Ven, 08/02/2013 - 05:01

The second defect (DPD200237626) is fixed in the Intel Fortran Composer XE 2013 Update 2 (2013.1.146 - Linux).

Still awaiting resolution of the first defect (DPD200237575).

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