gcc/libgomp/config/linux/proc.c

/* Copyright (C) 2005-2013 Free Software Foundation, Inc.
   Contributed by Jakub Jelinek <jakub@redhat.com>.

   This file is part of the GNU OpenMP Library (libgomp).

   Libgomp is free software; you can redistribute it and/or modify it
   under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3, or (at your option)
   any later version.

   Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
   more details.

   Under Section 7 of GPL version 3, you are granted additional
   permissions described in the GCC Runtime Library Exception, version
   3.1, as published by the Free Software Foundation.

   You should have received a copy of the GNU General Public License and
   a copy of the GCC Runtime Library Exception along with this program;
   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
   <http://www.gnu.org/licenses/>.  */

/* This file contains system specific routines related to counting
   online processors and dynamic load balancing.  */

#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#include "libgomp.h"
#include "proc.h"
#include <stdlib.h>
#include <unistd.h>
#ifdef HAVE_GETLOADAVG
# ifdef HAVE_SYS_LOADAVG_H
#  include <sys/loadavg.h>
# endif
#endif

#ifdef HAVE_PTHREAD_AFFINITY_NP
unsigned long
gomp_cpuset_popcount (cpu_set_t *cpusetp)
{
#ifdef CPU_COUNT
  /* glibc 2.6 and above provide a macro for this.  */
  return CPU_COUNT (cpusetp);
#else
  size_t i;
  unsigned long ret = 0;
  extern int check[sizeof (cpusetp->__bits[0]) == sizeof (unsigned long int)];

  (void) check;
  for (i = 0; i < sizeof (*cpusetp) / sizeof (cpusetp->__bits[0]); i++)
    {
      unsigned long int mask = cpusetp->__bits[i];
      if (mask == 0)
	continue;
      ret += __builtin_popcountl (mask);
    }
  return ret;
#endif
}
#endif

/* At startup, determine the default number of threads.  It would seem
   this should be related to the number of cpus online.  */

void
gomp_init_num_threads (void)
{
#ifdef HAVE_PTHREAD_AFFINITY_NP
  cpu_set_t cpuset;

  if (pthread_getaffinity_np (pthread_self (), sizeof (cpuset), &cpuset) == 0)
    {
      /* Count only the CPUs this process can use.  */
      gomp_global_icv.nthreads_var = gomp_cpuset_popcount (&cpuset);
      if (gomp_global_icv.nthreads_var == 0)
	gomp_global_icv.nthreads_var = 1;
      return;
    }
#endif
#ifdef _SC_NPROCESSORS_ONLN
  gomp_global_icv.nthreads_var = sysconf (_SC_NPROCESSORS_ONLN);
#endif
}

static int
get_num_procs (void)
{
#ifdef HAVE_PTHREAD_AFFINITY_NP
  cpu_set_t cpuset;

  if (gomp_cpu_affinity == NULL)
    {
      /* Count only the CPUs this process can use.  */
      if (pthread_getaffinity_np (pthread_self (), sizeof (cpuset),
				  &cpuset) == 0)
	{
	  int ret = gomp_cpuset_popcount (&cpuset);
	  return ret != 0 ? ret : 1;
	}
    }
  else
    {
      /* We can't use pthread_getaffinity_np in this case
	 (we have changed it ourselves, it binds to just one CPU).
	 Count instead the number of different CPUs we are
	 using.  gomp_init_affinity updated gomp_available_cpus to
	 the number of CPUs in the GOMP_AFFINITY mask that we are
	 allowed to use though.  */
      return gomp_available_cpus;
    }
#endif
#ifdef _SC_NPROCESSORS_ONLN
  return sysconf (_SC_NPROCESSORS_ONLN);
#else
  return gomp_icv (false)->nthreads_var;
#endif
}

/* When OMP_DYNAMIC is set, at thread launch determine the number of
   threads we should spawn for this team.  */
/* ??? I have no idea what best practice for this is.  Surely some
   function of the number of processors that are *still* online and
   the load average.  Here I use the number of processors online
   minus the 15 minute load average.  */

unsigned
gomp_dynamic_max_threads (void)
{
  unsigned n_onln, loadavg, nthreads_var = gomp_icv (false)->nthreads_var;

  n_onln = get_num_procs ();
  if (n_onln > nthreads_var)
    n_onln = nthreads_var;

  loadavg = 0;
#ifdef HAVE_GETLOADAVG
  {
    double dloadavg[3];
    if (getloadavg (dloadavg, 3) == 3)
      {
	/* Add 0.1 to get a kind of biased rounding.  */
	loadavg = dloadavg[2] + 0.1;
      }
  }
#endif

  if (loadavg >= n_onln)
    return 1;
  else
    return n_onln - loadavg;
}

int
omp_get_num_procs (void)
{
  return get_num_procs ();
}

ialias (omp_get_num_procs)