Is there a way to get a listing of variables and their scope (PRIVATE/SHARED in the OpenMP sense)?

Raghu Reddy

Tue, 06/19/2012 - 08:19

Hardware is an SGI ice system.
FORTRAN code with MPI+OpenMP.
There are multiple OpenMP regions.
There seems to be a problem with just one of them. If this particular routine is not compiled with OpenMP it runs fine on one thread or multiple threads.

With this region compiled with OpenMP:
- Code works with OMP_NUM_THREADS set to 1
- Crashes when set to anything other than 1

The region that has trouble has the following setup:
- There is a loop that has been parallelized using OpenMP.
- In the loop (hence in the parallel region) there is a chain of calls.

I want to know the scope of some of the variables in one of those routines.
I was wondering if it is possible to get this information.

Also, can the tools such as inspector be used in this situation (MPI+OpenMP codes)?

Any ideas on troubleshooting this problem?
Thanks

13 posts / 0 new

Last post

For more complete information about compiler optimizations, see our Optimization Notice.

jimdempseyatthecove

Tue, 06/19/2012 - 08:46

This "sounds" suspicious of you having an array/defined typedeclared in the subroutine/function containing "With this region compiled with OpenMP" that requires a SAVE attribute...
...OR...
The prior state of the code with an undesignated array/defined type, which when compiled without OpenMP or without RECURSIVE attribute behaves as if it had SAVE attribute, but when compiled with OpenMP behaves as if it has AUTOMATIC attribute (for non-master threads). Thus resulting in you having uninitialized variables for the non-master threads of that region.

...OR...

You are not using COPYIN in the appropriate place.

If nothing shows up as apparent along the above lines, then I suggest you insert some sanity checks into your code (ASSERTS as used in C/C++).

Jim Dempsey

Blog: The Parallel Void

www.quickthreadprogramming.com

Raghu Reddy

Tue, 06/19/2012 - 10:55

Thank you Jim!

In looking at the code some more, I see that the routines in question are "CONTAIN"ed in a module, and I do remeber a few months ago that I had seen problems with Intel compilers when using OpenMP with contained routines (this was in my previous job). In that case it was a simple code, and simply moving the "CONTAIN"ed routine outside the module solved the problem.

Is anyone aware of this issue? I wish I still had that simple code to post here.

I should clarify that in that simple example there weren't any "module variables" which would effectively be "save"d variables. In fact, in that simple case, it was simply a matter of moving that subroutine out of the module.

Thanks.

jimdempseyatthecove

Tue, 06/19/2012 - 12:14

subroutine foo
real :: array(123)
type(yourType) :: goo

In the above:

when NOT -openmp, array and goo are SAVE
when -openmp, the array and goo are on stack
(same applies without/with RECURSIVE on subroutine foo)

option switches can override this.

Check for any arrays and/or user defined types in the subroutine that is causing the issue.
There is another thread somewhere on this forum relating to

CONTAIN-ed subroutine having !$OMP PARALLEL...
.AND. when the main program does not establish the OpenMP thread pool.

If this is your case, try adding to your main (PROGRAM) before you call the CONTAIN'ed subroutine:

!$OMP PARALLEL
if(omp_get_thread_num() .eq. 999999) STOP
!$OMP END

The if test should always fail (not call stop), but is inserted there to assure the compiler does not optimize out dead code.

Jim Dempsey

Blog: The Parallel Void

www.quickthreadprogramming.com

TimP (Intel)

Tue, 06/19/2012 - 12:40

The symptoms you describe seem consistent with a shared variable or array which needs to be private. The usual way to get the compiler to give you hints is with omp default(none). Then the compiler will list as errors the variables where you didn't specify shared or private.
I've just been running Inspector, on an application which was checked by its predecessor several years ago. Inspector flagged a few scalar variables which needed private specification but hadn't been caught earlier, but it also missed some, and it missed local arrrays which needed private.
The usual recommendation on the Fortran forums is to add the RECURSIVE qualifier to all subroutines which will be called in a parallel region. An alternative is to compile with options which imply similar status for local variables and arrays (/Qauto or /Qopenmp for ifort, no /Qsave).

Raghu Reddy

Fri, 06/22/2012 - 14:24

I have located a simple example code that demonstrates this problem. The code and instructions for duplicating this problem is described below.

The example code segflts with ifc/12-12.1.0_sp1.6.233 and also ifc/12-12.0.4.191.
It runs successfully using gfortran.
The strange thing is function RMS is not even used!!!

Any suggestions? Thanks.

        program as43
        implicit none
!      ifort -openmp as43.f90 -o as43

!      set n=4; setenv OMP_NUM_THREADS ${n} ; time ./as43
        integer DIM

        parameter (DIM=4000)
        real v_old(0:DIM,0:DIM),v_new(0:DIM,0:DIM)

        integer i, j, k
        write (*,*) "DIM * DIM = ", DIM * DIM
        do i=0,DIM

           do j=0,DIM

              v_old(i, j) = 0.25

           enddo

        enddo
        do k=1,20             !do-loop over iterations.

!$omp parallel

!$omp do

           do j=1,(DIM-1)           !do-loops to generate new values for

              do i=1,(DIM-1)         ! all interior points.

                 v_new(i,j) = (v_old(i-1,j) + v_old(i+1,j) + v_old(i,j-1) + v_old(i,j+1))/4.0

              enddo

           enddo

!$omp end do

!$omp end parallel

        enddo    ! k loop
        print *, 'zzzzzzzzzz ', v_new(1,1)
      contains
       real function rms()
         integer i, j

         real myrms
         myrms = 0.d0
         do i=1,DIM-1

            do j=1,DIM-1

               myrms = myrms + (v_old(i,j)-v_new(i,j))**2

            enddo

         enddo
         rms = sqrt(myrms)/(DIM-1)
         return
       end function rms
     end program as43

jimdempseyatthecove

Fri, 06/22/2012 - 14:40

!$omp parallel private(j, i)

!$omp do

do j=1,(DIM-1) !do-loops to generate new values for

do i=1,(DIM-1) ! all interior points

Blog: The Parallel Void

www.quickthreadprogramming.com

Raghu Reddy

Fri, 06/22/2012 - 15:52

I was experimenting with a number of versions, I guess I pasted the wrong one.

But that does not change the result. I added this to the code, and it still fails same way.

!$omp parallel private(j,i) shared(v_old,v_new)
!$omp do

In fact just commenting out the unused routine makes it work!

Raghu Reddy

Mon, 06/25/2012 - 17:06

Anyone from Intel can help? Posted above is a complete code and instructions. Please be sure to make the correction pointed out by Jim.

Thanks.

Wander Gomes

Mon, 06/25/2012 - 19:58

Is possible to use C++ program language to list de variables?

Wander Gomes

Mon, 06/25/2012 - 20:00

What software are you use to compile the code?

TimP (Intel)

Thu, 06/28/2012 - 12:57

I don't see any major problem with this, assuming that you give it plenty of stack (under bash on linux,
ulimit -s unlimited).
As for minor problems, it seems a little out of line to nest your non-openmp loops backwards; the compiler may switch them automatically, since they are outside the parallel region.
Also, I usually take the precaution of setting -prec-div -prec-sqrt, and ifort takes that as preventing optimization of /4.0.

Raghu Reddy

Thu, 06/28/2012 - 16:25

You are right. The problem was the OMP_STACKSIZE (I don't remember the exact variable). Setting that to something reasonable makes it work.
Thanks again.

Back to original post

Intel® Developer Zone

Is there a way to get a listing of variables and their scope (PRIVATE/SHARED in the OpenMP sense)?

Is there a way to get a listing of variables and their scope (PRIVATE/SHARED in the OpenMP sense)?

Login to leave a comment.