1  /* Copyright (C) 2005-2023 Free Software Foundation, Inc.
       2     Contributed by Richard Henderson <rth@redhat.com>.
       3  
       4     This file is part of the GNU Offloading and Multi Processing Library
       5     (libgomp).
       6  
       7     Libgomp is free software; you can redistribute it and/or modify it
       8     under the terms of the GNU General Public License as published by
       9     the Free Software Foundation; either version 3, or (at your option)
      10     any later version.
      11  
      12     Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
      13     WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
      14     FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
      15     more details.
      16  
      17     Under Section 7 of GPL version 3, you are granted additional
      18     permissions described in the GCC Runtime Library Exception, version
      19     3.1, as published by the Free Software Foundation.
      20  
      21     You should have received a copy of the GNU General Public License and
      22     a copy of the GCC Runtime Library Exception along with this program;
      23     see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
      24     <http://www.gnu.org/licenses/>.  */
      25  
      26  /* This file contains system specific routines related to counting
      27     online processors and dynamic load balancing.  It is expected that
      28     a system may well want to write special versions of each of these.
      29  
      30     The following implementation uses a mix of POSIX and BSD routines.  */
      31  
      32  #include "libgomp.h"
      33  #include <unistd.h>
      34  #include <stdlib.h>
      35  #ifdef HAVE_GETLOADAVG
      36  # ifdef HAVE_SYS_LOADAVG_H
      37  #  include <sys/loadavg.h>
      38  # endif
      39  #endif
      40  #ifdef HAVE_SYS_SYSCTL_H
      41  # include <sys/sysctl.h>
      42  #endif
      43  
      44  static int
      45  get_num_procs (void)
      46  {
      47  #ifdef _SC_NPROCESSORS_ONLN
      48    return sysconf (_SC_NPROCESSORS_ONLN);
      49  #elif defined HW_NCPU
      50    int ncpus = 1;
      51    size_t len = sizeof(ncpus);
      52    sysctl((int[2]) {CTL_HW, HW_NCPU}, 2, &ncpus, &len, NULL, 0);
      53    return ncpus;
      54  #else
      55    return 0;
      56  #endif
      57  }
      58  
      59  /* At startup, determine the default number of threads.  It would seem
      60     this should be related to the number of cpus online.  */
      61  
      62  void
      63  gomp_init_num_threads (void)
      64  {
      65    int ncpus = get_num_procs ();
      66  
      67    if (ncpus > 0)
      68      gomp_global_icv.nthreads_var = ncpus;
      69  }
      70  
      71  /* When OMP_DYNAMIC is set, at thread launch determine the number of
      72     threads we should spawn for this team.  */
      73  /* ??? I have no idea what best practice for this is.  Surely some
      74     function of the number of processors that are *still* online and
      75     the load average.  Here I use the number of processors online
      76     minus the 15 minute load average.  */
      77  
      78  unsigned
      79  gomp_dynamic_max_threads (void)
      80  {
      81    unsigned n_onln, loadavg;
      82    unsigned nthreads_var = gomp_icv (false)->nthreads_var;
      83  
      84    n_onln = get_num_procs ();
      85    if (!n_onln || n_onln > nthreads_var)
      86      n_onln = nthreads_var;
      87  
      88    loadavg = 0;
      89  #ifdef HAVE_GETLOADAVG
      90    {
      91      double dloadavg[3];
      92      if (getloadavg (dloadavg, 3) == 3)
      93        {
      94  	/* Add 0.1 to get a kind of biased rounding.  */
      95  	loadavg = dloadavg[2] + 0.1;
      96        }
      97    }
      98  #endif
      99  
     100    if (loadavg >= n_onln)
     101      return 1;
     102    else
     103      return n_onln - loadavg;
     104  }
     105  
     106  int
     107  omp_get_num_procs (void)
     108  {
     109    int ncpus = get_num_procs ();
     110    if (ncpus <= 0)
     111      ncpus = gomp_icv (false)->nthreads_var;
     112    return ncpus;
     113  }
     114  
     115  ialias (omp_get_num_procs)