CODEWITHSUNDEEP
openacc
Steve
Steve

Reputation: 89

Global Variables in OpenACC

I'm trying to handle a global variable declared in this way in head.h:

extern int NX1_TOT;
#pragma acc declare create(NX1_TOT)

While in globals.h:

int NX1_TOT;

in main.c:

#include "head.h"
#include "globals.h"

In the file initialize.c I set the NX1_TOT value:

NX1_TOT=ntot[IDIR];

What happens is that if I try to print the value of NX1_TOT in different kernels, I get different and sometimes wrong results. I tried with #pragma acc update device but it doesn't seem to make a difference. I just want to be able to use a variable (that is set at the beginning of the application and never modified) in every device kernel without having to pass it as an argument to every routine (seems a very simple problem to me but the documentation is null).

Upvotes: 0

Views: 46

Answers (1)

Mat Colgrove
Mat Colgrove

Reputation: 5646

Can you please provide a minimal reproducing test case? This should work as expected, but without an example we can't tell what the code is doing.

Here's a simple working example you can start with and then modify to show how your code is doing the operations.

% cat head.h
#include <stdlib.h>
#include <stdio.h>

extern int NX1_TOT;
#pragma acc declare create(NX1_TOT)
% cat globals.h
int NX1_TOT;
% cat test.c

#include "head.h"
#include "globals.h"

int main() {

   int *A;
   A=(int*) malloc(sizeof(int)*1024);

   NX1_TOT=2;
#pragma acc update device(NX1_TOT)

#pragma acc parallel loop copyout(A[:1024])
  for (int i=0; i<1024; ++i) {
      A[i] = NX1_TOT;
  }

  printf("%d %d\n", A[10],A[100]);
  free(A);
}
% nvc test.c -acc -Minfo=accel; a.out
main:
     10, Generating update device(NX1_TOT)
         Generating copyout(A[:1024]) [if not already present]
         Generating NVIDIA GPU code
         14, #pragma acc loop gang, vector(128) /* blockIdx.x threadIdx.x */
2 2

Upvotes: 0

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