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From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libgomp/58691] New: OpenMP 4: Surprising results with OMP_PLACES=
Date: Fri, 11 Oct 2013 20:03:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58691

            Bug ID: 58691
           Summary: OpenMP 4: Surprising results with OMP_PLACES=
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          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

I played around with OMP_PLACES and noticed the following oddness:


First, create some OpenMP program:
$  echo "end" > test.f90; gfortran -fopenmp test.f90


Using "threads", "cores" or "sockets", one gets a places result:

$ OMP_PLACES='threads' OMP_DISPLAY_ENV=verbose ./a.out 2>&1 |grep OMP_PLACES
  OMP_PLACES = '{0},{1},{2},{3}'


However, if one specifies a numerical value, one doesn't:

$ OMP_PLACES='{0:2}' OMP_DISPLAY_ENV=verbose ./a.out 2>&1 |grep OMP_PLACES
  OMP_PLACES = ''



The reason - as it turns out - is that one has in libgomp/env.c the following
code:


parse_places_var (const char *name)
{
...
  if (strncasecmp (env, "threads", 7) == 0)
    {
      env += 7;
      level = 1;
    }
...
  if (level)
    {
...
      return gomp_affinity_init_level (level, count, false);
    }

...

  if (gomp_global_icv.bind_var == omp_proc_bind_false)
    return false;

  gomp_places_list_len = 0;
  gomp_places_list = gomp_affinity_alloc (count, false);



Namely: If OMP_PROC_BIND is FALSE, which is the default, the affinity does not
get set.


 * * *

I think in terms of the OpenMP spec, everything is implementation defined.
Nonetheless, the following should match common expectations:


* Both ways of setting OMP_PLACES should act identically.

* If the user has set OMP_PLACES, the default of OMP_PROC_BIND should change to
TRUE.

* If the user has explicitly set OMP_PROC_BIND=FALSE, OMP_PLACES should be
ignored.


* Probably, a few words in libgomp.text's OMP_PROC_BIND or OMP_PLACES to the
interaction of the two wouldn't harm either.