2 * SPDX-License-Identifier: LGPL-2.1-only
4 * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
5 * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
13 int __num_possible_cpus
;
15 #if (defined(__GLIBC__) || defined( __UCLIBC__))
16 void _get_num_possible_cpus(void)
20 /* On Linux, when some processors are offline
21 * _SC_NPROCESSORS_CONF counts the offline
22 * processors, whereas _SC_NPROCESSORS_ONLN
23 * does not. If we used _SC_NPROCESSORS_ONLN,
24 * getcpu() could return a value greater than
25 * this sysconf, in which case the arrays
26 * indexed by processor would overflow.
28 result
= sysconf(_SC_NPROCESSORS_CONF
);
31 __num_possible_cpus
= result
;
37 * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not
38 * return the number of configured CPUs in the system but relies on the cpu
39 * affinity mask of the current task.
41 * So instead we use a strategy similar to GLIBC's, counting the cpu
42 * directories in "/sys/devices/system/cpu" and fallback on the value from
43 * sysconf if it fails.
50 #include <sys/types.h>
52 #define __max(a,b) ((a)>(b)?(a):(b))
54 void _get_num_possible_cpus(void)
56 int result
, count
= 0;
60 cpudir
= opendir("/sys/devices/system/cpu");
65 * Count the number of directories named "cpu" followed by and
66 * integer. This is the same strategy as glibc uses.
68 while ((entry
= readdir(cpudir
))) {
69 if (entry
->d_type
== DT_DIR
&&
70 strncmp(entry
->d_name
, "cpu", 3) == 0) {
73 unsigned long cpu_num
;
75 cpu_num
= strtoul(entry
->d_name
+ 3, &endptr
, 10);
76 if ((cpu_num
< ULONG_MAX
) && (endptr
!= entry
->d_name
+ 3)
77 && (*endptr
== '\0')) {
85 * Get the sysconf value as a fallback. Keep the highest number.
87 result
= __max(sysconf(_SC_NPROCESSORS_CONF
), count
);
90 * If both methods failed, don't store the value.
94 __num_possible_cpus
= result
;
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