| 1 | /* |
| 2 | * libringbuffer/smp.c |
| 3 | * |
| 4 | * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 5 | * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com> |
| 6 | * |
| 7 | * This library is free software; you can redistribute it and/or |
| 8 | * modify it under the terms of the GNU Lesser General Public |
| 9 | * License as published by the Free Software Foundation; only |
| 10 | * version 2.1 of the License. |
| 11 | * |
| 12 | * This library is distributed in the hope that it will be useful, |
| 13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 15 | * Lesser General Public License for more details. |
| 16 | * |
| 17 | * You should have received a copy of the GNU Lesser General Public |
| 18 | * License along with this library; if not, write to the Free Software |
| 19 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 20 | */ |
| 21 | |
| 22 | #define _GNU_SOURCE |
| 23 | #define _LGPL_SOURCE |
| 24 | #include <unistd.h> |
| 25 | #include <pthread.h> |
| 26 | #include "smp.h" |
| 27 | |
| 28 | int __num_possible_cpus; |
| 29 | |
| 30 | #if (defined(__GLIBC__) || defined( __UCLIBC__)) |
| 31 | void _get_num_possible_cpus(void) |
| 32 | { |
| 33 | int result; |
| 34 | |
| 35 | /* On Linux, when some processors are offline |
| 36 | * _SC_NPROCESSORS_CONF counts the offline |
| 37 | * processors, whereas _SC_NPROCESSORS_ONLN |
| 38 | * does not. If we used _SC_NPROCESSORS_ONLN, |
| 39 | * getcpu() could return a value greater than |
| 40 | * this sysconf, in which case the arrays |
| 41 | * indexed by processor would overflow. |
| 42 | */ |
| 43 | result = sysconf(_SC_NPROCESSORS_CONF); |
| 44 | if (result == -1) |
| 45 | return; |
| 46 | __num_possible_cpus = result; |
| 47 | } |
| 48 | |
| 49 | #else |
| 50 | |
| 51 | /* |
| 52 | * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not |
| 53 | * return the number of configured CPUs in the system but relies on the cpu |
| 54 | * affinity mask of the current task. |
| 55 | * |
| 56 | * So instead we use a strategy similar to GLIBC's, counting the cpu |
| 57 | * directories in "/sys/devices/system/cpu" and fallback on the value from |
| 58 | * sysconf if it fails. |
| 59 | */ |
| 60 | |
| 61 | #include <dirent.h> |
| 62 | #include <limits.h> |
| 63 | #include <stdlib.h> |
| 64 | #include <string.h> |
| 65 | #include <sys/types.h> |
| 66 | |
| 67 | #define __max(a,b) ((a)>(b)?(a):(b)) |
| 68 | |
| 69 | void _get_num_possible_cpus(void) |
| 70 | { |
| 71 | int result, count = 0; |
| 72 | DIR *cpudir; |
| 73 | struct dirent *entry; |
| 74 | |
| 75 | cpudir = opendir("/sys/devices/system/cpu"); |
| 76 | if (cpudir == NULL) |
| 77 | goto end; |
| 78 | |
| 79 | /* |
| 80 | * Count the number of directories named "cpu" followed by and |
| 81 | * integer. This is the same strategy as glibc uses. |
| 82 | */ |
| 83 | while ((entry = readdir(cpudir))) { |
| 84 | if (entry->d_type == DT_DIR && |
| 85 | strncmp(entry->d_name, "cpu", 3) == 0) { |
| 86 | |
| 87 | char *endptr; |
| 88 | unsigned long cpu_num; |
| 89 | |
| 90 | cpu_num = strtoul(entry->d_name + 3, &endptr, 10); |
| 91 | if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3) |
| 92 | && (*endptr == '\0')) { |
| 93 | count++; |
| 94 | } |
| 95 | } |
| 96 | } |
| 97 | |
| 98 | end: |
| 99 | /* |
| 100 | * Get the sysconf value as a fallback. Keep the highest number. |
| 101 | */ |
| 102 | result = __max(sysconf(_SC_NPROCESSORS_CONF), count); |
| 103 | |
| 104 | /* |
| 105 | * If both methods failed, don't store the value. |
| 106 | */ |
| 107 | if (result < 1) |
| 108 | return; |
| 109 | __num_possible_cpus = result; |
| 110 | } |
| 111 | #endif |