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