Move all sources to 'src/'
[lttng-ust.git] / src / libringbuffer / smp.c
1 /*
2 * SPDX-License-Identifier: LGPL-2.1-only
3 *
4 * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
5 * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
6 */
7
8 #define _LGPL_SOURCE
9 #include <unistd.h>
10 #include <pthread.h>
11 #include "smp.h"
12
13 int __num_possible_cpus;
14
15 #if (defined(__GLIBC__) || defined( __UCLIBC__))
16 void _get_num_possible_cpus(void)
17 {
18 int result;
19
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.
27 */
28 result = sysconf(_SC_NPROCESSORS_CONF);
29 if (result == -1)
30 return;
31 __num_possible_cpus = result;
32 }
33
34 #else
35
36 /*
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.
40 *
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.
44 */
45
46 #include <dirent.h>
47 #include <limits.h>
48 #include <stdlib.h>
49 #include <string.h>
50 #include <sys/types.h>
51
52 #define __max(a,b) ((a)>(b)?(a):(b))
53
54 void _get_num_possible_cpus(void)
55 {
56 int result, count = 0;
57 DIR *cpudir;
58 struct dirent *entry;
59
60 cpudir = opendir("/sys/devices/system/cpu");
61 if (cpudir == NULL)
62 goto end;
63
64 /*
65 * Count the number of directories named "cpu" followed by and
66 * integer. This is the same strategy as glibc uses.
67 */
68 while ((entry = readdir(cpudir))) {
69 if (entry->d_type == DT_DIR &&
70 strncmp(entry->d_name, "cpu", 3) == 0) {
71
72 char *endptr;
73 unsigned long cpu_num;
74
75 cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
76 if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
77 && (*endptr == '\0')) {
78 count++;
79 }
80 }
81 }
82
83 end:
84 /*
85 * Get the sysconf value as a fallback. Keep the highest number.
86 */
87 result = __max(sysconf(_SC_NPROCESSORS_CONF), count);
88
89 /*
90 * If both methods failed, don't store the value.
91 */
92 if (result < 1)
93 return;
94 __num_possible_cpus = result;
95 }
96 #endif
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