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