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  
      41  
      42  /* At startup, determine the default number of threads.  It would seem
      43     this should be related to the number of cpus online.  */
      44  
      45  void
      46  gomp_init_num_threads (void)
      47  {
      48  #ifdef _SC_NPROCESSORS_ONLN
      49    gomp_global_icv.nthreads_var = sysconf (_SC_NPROCESSORS_ONLN);
      50  #endif
      51  }
      52  
      53  /* When OMP_DYNAMIC is set, at thread launch determine the number of
      54     threads we should spawn for this team.  */
      55  /* ??? I have no idea what best practice for this is.  Surely some
      56     function of the number of processors that are *still* online and
      57     the load average.  Here I use the number of processors online
      58     minus the 15 minute load average.  */
      59  
      60  unsigned
      61  gomp_dynamic_max_threads (void)
      62  {
      63    unsigned n_onln, loadavg;
      64    unsigned nthreads_var = gomp_icv (false)->nthreads_var;
      65  
      66  #ifdef _SC_NPROCESSORS_ONLN
      67    n_onln = sysconf (_SC_NPROCESSORS_ONLN);
      68    if (n_onln > nthreads_var)
      69      n_onln = nthreads_var;
      70  #else
      71    n_onln = nthreads_var;
      72  #endif
      73  
      74    loadavg = 0;
      75  #ifdef HAVE_GETLOADAVG
      76    {
      77      double dloadavg[3];
      78      if (getloadavg (dloadavg, 3) == 3)
      79        {
      80  	/* Add 0.1 to get a kind of biased rounding.  */
      81  	loadavg = dloadavg[2] + 0.1;
      82        }
      83    }
      84  #endif
      85  
      86    if (loadavg >= n_onln)
      87      return 1;
      88    else
      89      return n_onln - loadavg;
      90  }
      91  
      92  int
      93  omp_get_num_procs (void)
      94  {
      95  #ifdef _SC_NPROCESSORS_ONLN
      96    return sysconf (_SC_NPROCESSORS_ONLN);
      97  #else
      98    return gomp_icv (false)->nthreads_var;
      99  #endif
     100  }
     101  
     102  ialias (omp_get_num_procs)