libcounter/smp.c

   1 /*
   2  * libcounter/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 __lttng_counter_num_possible_cpus;
  29
  30 #if (defined(__GLIBC__) || defined( __UCLIBC__))
  31 void _lttng_counter_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         __lttng_counter_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 _lttng_counter_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         __lttng_counter_num_possible_cpus = result;
 110 }
 111 #endif