libcounter/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
  10 #include <unistd.h>
  11 #include <pthread.h>
  12 #include "smp.h"
  13
  14 int __lttng_counter_num_possible_cpus;
  15
  16 #if (defined(__GLIBC__) || defined( __UCLIBC__))
  17 void _lttng_counter_get_num_possible_cpus(void)
  18 {
  19         int result;
  20
  21         /* On Linux, when some processors are offline
  22          * _SC_NPROCESSORS_CONF counts the offline
  23          * processors, whereas _SC_NPROCESSORS_ONLN
  24          * does not. If we used _SC_NPROCESSORS_ONLN,
  25          * getcpu() could return a value greater than
  26          * this sysconf, in which case the arrays
  27          * indexed by processor would overflow.
  28          */
  29         result = sysconf(_SC_NPROCESSORS_CONF);
  30         if (result == -1)
  31                 return;
  32         __lttng_counter_num_possible_cpus = result;
  33 }
  34
  35 #else
  36
  37 /*
  38  * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not
  39  * return the number of configured CPUs in the system but relies on the cpu
  40  * affinity mask of the current task.
  41  *
  42  * So instead we use a strategy similar to GLIBC's, counting the cpu
  43  * directories in "/sys/devices/system/cpu" and fallback on the value from
  44  * sysconf if it fails.
  45  */
  46
  47 #include <dirent.h>
  48 #include <limits.h>
  49 #include <stdlib.h>
  50 #include <string.h>
  51 #include <sys/types.h>
  52
  53 #define __max(a,b) ((a)>(b)?(a):(b))
  54
  55 void _lttng_counter_get_num_possible_cpus(void)
  56 {
  57         int result, count = 0;
  58         DIR *cpudir;
  59         struct dirent *entry;
  60
  61         cpudir = opendir("/sys/devices/system/cpu");
  62         if (cpudir == NULL)
  63                 goto end;
  64
  65         /*
  66          * Count the number of directories named "cpu" followed by and
  67          * integer. This is the same strategy as glibc uses.
  68          */
  69         while ((entry = readdir(cpudir))) {
  70                 if (entry->d_type == DT_DIR &&
  71                         strncmp(entry->d_name, "cpu", 3) == 0) {
  72
  73                         char *endptr;
  74                         unsigned long cpu_num;
  75
  76                         cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
  77                         if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
  78                                         && (*endptr == '\0')) {
  79                                 count++;
  80                         }
  81                 }
  82         }
  83
  84 end:
  85         /*
  86          * Get the sysconf value as a fallback. Keep the highest number.
  87          */
  88         result = __max(sysconf(_SC_NPROCESSORS_CONF), count);
  89
  90         /*
  91          * If both methods failed, don't store the value.
  92          */
  93         if (result < 1)
  94                 return;
  95         __lttng_counter_num_possible_cpus = result;
  96 }
  97 #endif