Remove duplicated 'smp' code

[lttng-ust.git] / src / common / smp.c

diff --git a/src/common/smp.c b/src/common/smp.c
new file mode 100644 (file)
index 0000000..95f6dd1
--- /dev/null
+++ b/src/common/smp.c
@@ -0,0 +1,113 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-only
+ *
+ * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
+ */
+
+#define _LGPL_SOURCE
+#include <unistd.h>
+#include <pthread.h>
+
+#include <urcu/compiler.h>
+
+#include "common/smp.h"
+
+static int num_possible_cpus_cache;
+
+#if (defined(__GLIBC__) || defined( __UCLIBC__))
+static void _get_num_possible_cpus(void)
+{
+       int result;
+
+       /* On Linux, when some processors are offline
+        * _SC_NPROCESSORS_CONF counts the offline
+        * processors, whereas _SC_NPROCESSORS_ONLN
+        * does not. If we used _SC_NPROCESSORS_ONLN,
+        * getcpu() could return a value greater than
+        * this sysconf, in which case the arrays
+        * indexed by processor would overflow.
+        */
+       result = sysconf(_SC_NPROCESSORS_CONF);
+       if (result == -1)
+               return;
+       num_possible_cpus_cache = result;
+}
+
+#else
+
+/*
+ * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not
+ * return the number of configured CPUs in the system but relies on the cpu
+ * affinity mask of the current task.
+ *
+ * So instead we use a strategy similar to GLIBC's, counting the cpu
+ * directories in "/sys/devices/system/cpu" and fallback on the value from
+ * sysconf if it fails.
+ */
+
+#include <dirent.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+
+#define __max(a,b) ((a)>(b)?(a):(b))
+
+static void _get_num_possible_cpus(void)
+{
+       int result, count = 0;
+       DIR *cpudir;
+       struct dirent *entry;
+
+       cpudir = opendir("/sys/devices/system/cpu");
+       if (cpudir == NULL)
+               goto end;
+
+       /*
+        * Count the number of directories named "cpu" followed by and
+        * integer. This is the same strategy as glibc uses.
+        */
+       while ((entry = readdir(cpudir))) {
+               if (entry->d_type == DT_DIR &&
+                       strncmp(entry->d_name, "cpu", 3) == 0) {
+
+                       char *endptr;
+                       unsigned long cpu_num;
+
+                       cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
+                       if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
+                                       && (*endptr == '\0')) {
+                               count++;
+                       }
+               }
+       }
+
+end:
+       /*
+        * Get the sysconf value as a fallback. Keep the highest number.
+        */
+       result = __max(sysconf(_SC_NPROCESSORS_CONF), count);
+
+       /*
+        * If both methods failed, don't store the value.
+        */
+       if (result < 1)
+               return;
+       num_possible_cpus_cache = result;
+}
+#endif
+
+/*
+ * Returns the total number of CPUs in the system. If the cache is not yet
+ * initialized, get the value from the system through sysconf and cache it.
+ *
+ * If the sysconf call fails, don't populate the cache and return 0.
+ */
+int num_possible_cpus(void)
+{
+       if (caa_unlikely(!num_possible_cpus_cache))
+               _get_num_possible_cpus();
+
+       return num_possible_cpus_cache;
+}