libgomp/config/posix/proc.c

   1 /* Copyright (C) 2005-2018 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)