https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109875
Bug ID: 109875
Summary: [OpenMP] nteams-var / OMP_NUM_TEAMS → ICV not passed
to the device / default value
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Keywords: openmp
Severity: normal
Priority: P3
Component: libgomp
Assignee: unassigned at gcc dot gnu.org
Reporter: burnus at gcc dot gnu.org
CC: jakub at gcc dot gnu.org
Target Milestone: ---
Related: https://github.com/SOLLVE/sollve_vv/pull/728 and
OpenMP Spec Issue 3619.
The following is with host fallback - and I might miss something because of
this.
However, I get only a single team with the following code;
even though max_num_teams == 3.
Replacing the set_num_teams by
OMP_NUM_TEAMS=7 OMP_NUM_TEAMS_DEV=8
will yield the expected 7 for max_teams.
But it will still execute with a single team. — Using num_teams(3) as clause
will have an effect, however.
TODO:
* Check whether TEAMS = 1 makes sense for host fallback
and what the result is with actual offloading.
EXPECTED:
* The value of the ICV is honored on the device side
* Possibly, the initial value should be not 0 but a different value,
but that depends on the OpenMP Spec Issue 3619.
NOTE: While the init value is now changed, as omp_get_max_teams()
is confusingly written, just changing the default is undetectable
inside the program as only omp_get_max_teams() or display-env can be
used to determine the value - and the values returned by the latter
is not really available for consumption inside of the program.
* On the host side, the default seems to be 3, given that there is:
libgomp/teams.c: num_teams = gomp_nteams_var ? gomp_nteams_var : 3;
It seems as if get_gomp_offload_icvs sets the ICV for the device but it does
not seem to get actually get used. – At least not for host fallback.
#include <omp.h>
int main ()
{
int num_teams;
#if 1 // set to 0 to test the environment variables
omp_set_num_teams(2);
#pragma omp target
omp_set_num_teams(3);
#endif
__builtin_printf("max_teams: %d\n", omp_get_max_teams());
#pragma omp target teams map(tofrom: num_teams) //num_teams(4)
{
if (omp_get_team_num() == 0) {
num_teams = omp_get_num_teams();
}
}
__builtin_printf("num_teams: %d\n", num_teams);
return 0;
}
