src/common/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 <assert.h>
  10 #include <ctype.h>
  11 #include <errno.h>
  12 #include <fcntl.h>
  13 #include <limits.h>
  14 #include <unistd.h>
  15 #include <pthread.h>
  16 #include <stdlib.h>
  17
  18 #include <urcu/compiler.h>
  19
  20 #include "common/logging.h"
  21 #include "common/smp.h"
  22
  23 static int num_possible_cpus_cache;
  24
  25 #if (defined(__GLIBC__) || defined( __UCLIBC__))
  26 int get_num_possible_cpus_fallback(void)
  27 {
  28         /* On Linux, when some processors are offline
  29          * _SC_NPROCESSORS_CONF counts the offline
  30          * processors, whereas _SC_NPROCESSORS_ONLN
  31          * does not. If we used _SC_NPROCESSORS_ONLN,
  32          * getcpu() could return a value greater than
  33          * this sysconf, in which case the arrays
  34          * indexed by processor would overflow.
  35          */
  36         return sysconf(_SC_NPROCESSORS_CONF);
  37 }
  38
  39 #else
  40
  41 /*
  42  * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not
  43  * return the number of configured CPUs in the system but relies on the cpu
  44  * affinity mask of the current task.
  45  *
  46  * So instead we use a strategy similar to GLIBC's, counting the cpu
  47  * directories in "/sys/devices/system/cpu" and fallback on the value from
  48  * sysconf if it fails.
  49  */
  50
  51 #include <dirent.h>
  52 #include <limits.h>
  53 #include <stdlib.h>
  54 #include <string.h>
  55 #include <sys/types.h>
  56
  57 #define __max(a,b) ((a)>(b)?(a):(b))
  58
  59 int get_num_possible_cpus_fallback(void)
  60 {
  61         int count = 0;
  62         DIR *cpudir;
  63         struct dirent *entry;
  64
  65         cpudir = opendir("/sys/devices/system/cpu");
  66         if (cpudir == NULL)
  67                 goto end;
  68
  69         /*
  70          * Count the number of directories named "cpu" followed by and
  71          * integer. This is the same strategy as glibc uses.
  72          */
  73         while ((entry = readdir(cpudir))) {
  74                 if (entry->d_type == DT_DIR &&
  75                         strncmp(entry->d_name, "cpu", 3) == 0) {
  76
  77                         char *endptr;
  78                         unsigned long cpu_num;
  79
  80                         cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
  81                         if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
  82                                         && (*endptr == '\0')) {
  83                                 count++;
  84                         }
  85                 }
  86         }
  87
  88 end:
  89         /*
  90          * Get the sysconf value as a fallback. Keep the highest number.
  91          */
  92         return __max(sysconf(_SC_NPROCESSORS_CONF), count);
  93 }
  94 #endif
  95
  96 /*
  97  * Get the CPU possible mask string from sysfs.
  98  *
  99  * buf: the buffer where the mask will be read.
 100  * max_bytes: the maximum number of bytes to write in the buffer.
 101  *
 102  * Returns the number of bytes read or -1 on error.
 103  */
 104 int get_possible_cpu_mask_from_sysfs(char *buf, size_t max_bytes)
 105 {
 106         ssize_t bytes_read = 0;
 107         size_t total_bytes_read = 0;
 108         int fd = -1, ret = -1;
 109
 110         if (buf == NULL)
 111                 goto end;
 112
 113         fd = open("/sys/devices/system/cpu/possible", O_RDONLY);
 114         if (fd < 0)
 115                 goto end;
 116
 117         do {
 118                 bytes_read = read(fd, buf + total_bytes_read,
 119                                 max_bytes - total_bytes_read);
 120
 121                 if (bytes_read < 0) {
 122                         if (errno == EINTR) {
 123                                 continue;       /* retry operation */
 124                         } else {
 125                                 goto end;
 126                         }
 127                 }
 128
 129                 total_bytes_read += bytes_read;
 130                 assert(total_bytes_read <= max_bytes);
 131         } while (max_bytes > total_bytes_read && bytes_read > 0);
 132
 133         /*
 134          * Make sure the mask read is a null terminated string.
 135          */
 136         if (total_bytes_read < max_bytes)
 137                 buf[total_bytes_read] = '\0';
 138         else
 139                 buf[max_bytes - 1] = '\0';
 140
 141         if (total_bytes_read > INT_MAX)
 142                 goto end;
 143         ret = (int) total_bytes_read;
 144 end:
 145         if (fd >= 0 && close(fd) < 0)
 146                 PERROR("close");
 147         return ret;
 148 }
 149
 150 /*
 151  * Get the number of CPUs from the possible cpu mask.
 152  *
 153  * pmask: the mask to parse.
 154  * len: the len of the mask excluding '\0'.
 155  *
 156  * Returns the number of possible CPUs from the mask or 0 on error.
 157  */
 158 int get_num_possible_cpus_from_mask(const char *pmask, size_t len)
 159 {
 160         ssize_t i;
 161         unsigned long cpu_index;
 162         char *endptr;
 163
 164         /* We need at least one char to read */
 165         if (len < 1)
 166                 goto error;
 167
 168         /* Start from the end to read the last CPU index. */
 169         for (i = len - 1; i > 0; i--) {
 170                 /* Break when we hit the first separator. */
 171                 if ((pmask[i] == ',') || (pmask[i] == '-')) {
 172                         i++;
 173                         break;
 174                 }
 175         }
 176
 177         cpu_index = strtoul(&pmask[i], &endptr, 10);
 178
 179         /*
 180          * If we read a CPU index, increment it by one to return a number of
 181          * CPUs.
 182          */
 183         if ((&pmask[i] != endptr) && (cpu_index < INT_MAX))
 184                 return (int) cpu_index + 1;
 185
 186 error:
 187         return 0;
 188 }
 189
 190 static void _get_num_possible_cpus(void)
 191 {
 192         int ret;
 193         char buf[LTTNG_UST_CPUMASK_SIZE];
 194
 195         /* Get the possible cpu mask from sysfs, fallback to sysconf. */
 196         ret = get_possible_cpu_mask_from_sysfs((char *) &buf, LTTNG_UST_CPUMASK_SIZE);
 197         if (ret <= 0)
 198                 goto fallback;
 199
 200         /* Parse the possible cpu mask, on failure fallback to sysconf. */
 201         ret = get_num_possible_cpus_from_mask((char *) &buf, ret);
 202         if (ret > 0)
 203                 goto end;
 204
 205 fallback:
 206         /* Fallback to sysconf. */
 207         ret = get_num_possible_cpus_fallback();
 208
 209 end:
 210         /* If all methods failed, don't store the value. */
 211         if (ret < 1)
 212                 return;
 213
 214         num_possible_cpus_cache = ret;
 215 }
 216
 217 /*
 218  * Returns the total number of CPUs in the system. If the cache is not yet
 219  * initialized, get the value from "/sys/devices/system/cpu/possible" or
 220  * fallback to sysconf and cache it.
 221  *
 222  * If all methods fail, don't populate the cache and return 0.
 223  */
 224 int num_possible_cpus(void)
 225 {
 226         if (caa_unlikely(!num_possible_cpus_cache))
 227                 _get_num_possible_cpus();
 228
 229         return num_possible_cpus_cache;
 230 }