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/* Copyright (C) 2005-2022 Free Software Foundation, Inc.
Contributed by Richard Henderson <>.
This file is part of the GNU Offloading and Multi Processing Library
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
<>. */
/* This file contains system specific routines related to counting
online processors and dynamic load balancing. It is expected that
a system may well want to write special versions of each of these.
The following implementation uses a mix of POSIX and BSD routines. */
#include "libgomp.h"
#include <unistd.h>
#include <stdlib.h>
# include <sys/loadavg.h>
# endif
# include <sys/sysctl.h>
static int
get_num_procs (void)
return sysconf (_SC_NPROCESSORS_ONLN);
#elif defined HW_NCPU
int ncpus = 1;
size_t len = sizeof(ncpus);
sysctl((int[2]) {CTL_HW, HW_NCPU}, 2, &ncpus, &len, NULL, 0);
return ncpus;
return 0;
/* At startup, determine the default number of threads. It would seem
this should be related to the number of cpus online. */
gomp_init_num_threads (void)
int ncpus = get_num_procs ();
if (ncpus > 0)
gomp_global_icv.nthreads_var = ncpus;
/* 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. */
gomp_dynamic_max_threads (void)
unsigned n_onln, loadavg;
unsigned nthreads_var = gomp_icv (false)->nthreads_var;
n_onln = get_num_procs ();
if (!n_onln || n_onln > nthreads_var)
n_onln = nthreads_var;
loadavg = 0;
double dloadavg[3];
if (getloadavg (dloadavg, 3) == 3)
/* Add 0.1 to get a kind of biased rounding. */
loadavg = dloadavg[2] + 0.1;
if (loadavg >= n_onln)
return 1;
return n_onln - loadavg;
omp_get_num_procs (void)
int ncpus = get_num_procs ();
if (ncpus <= 0)
ncpus = gomp_icv (false)->nthreads_var;
return ncpus;
ialias (omp_get_num_procs)