libringbuffer/smp.c

   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 _LGPL_SOURCE
  23 #include <unistd.h>
  24 #include <pthread.h>
  25 #include "smp.h"
  26
  27 int __num_possible_cpus;
  28
  29 #if (defined(__GLIBC__) || defined( __UCLIBC__))
  30 void _get_num_possible_cpus(void)
  31 {
  32         int result;
  33
  34         /* On Linux, when some processors are offline
  35          * _SC_NPROCESSORS_CONF counts the offline
  36          * processors, whereas _SC_NPROCESSORS_ONLN
  37          * does not. If we used _SC_NPROCESSORS_ONLN,
  38          * getcpu() could return a value greater than
  39          * this sysconf, in which case the arrays
  40          * indexed by processor would overflow.
  41          */
  42         result = sysconf(_SC_NPROCESSORS_CONF);
  43         if (result == -1)
  44                 return;
  45         __num_possible_cpus = result;
  46 }
  47
  48 #else
  49
  50 /*
  51  * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not
  52  * return the number of configured CPUs in the system but relies on the cpu
  53  * affinity mask of the current task.
  54  *
  55  * So instead we use a strategy similar to GLIBC's, counting the cpu
  56  * directories in "/sys/devices/system/cpu" and fallback on the value from
  57  * sysconf if it fails.
  58  */
  59
  60 #include <dirent.h>
  61 #include <limits.h>
  62 #include <stdlib.h>
  63 #include <string.h>
  64 #include <sys/types.h>
  65
  66 #define __max(a,b) ((a)>(b)?(a):(b))
  67
  68 void _get_num_possible_cpus(void)
  69 {
  70         int result, count = 0;
  71         DIR *cpudir;
  72         struct dirent *entry;
  73
  74         cpudir = opendir("/sys/devices/system/cpu");
  75         if (cpudir == NULL)
  76                 goto end;
  77
  78         /*
  79          * Count the number of directories named "cpu" followed by and
  80          * integer. This is the same strategy as glibc uses.
  81          */
  82         while ((entry = readdir(cpudir))) {
  83                 if (entry->d_type == DT_DIR &&
  84                         strncmp(entry->d_name, "cpu", 3) == 0) {
  85
  86                         char *endptr;
  87                         unsigned long cpu_num;
  88
  89                         cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
  90                         if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
  91                                         && (*endptr == '\0')) {
  92                                 count++;
  93                         }
  94                 }
  95         }
  96
  97 end:
  98         /*
  99          * Get the sysconf value as a fallback. Keep the highest number.
 100          */
 101         result = __max(sysconf(_SC_NPROCESSORS_CONF), count);
 102
 103         /*
 104          * If both methods failed, don't store the value.
 105          */
 106         if (result < 1)
 107                 return;
 108         __num_possible_cpus = result;
 109 }
 110 #endif