Implement lttng_ust_get_cpu()

[lttng-ust.git] / libringbuffer / getcpu.h

diff --git a/libringbuffer/getcpu.h b/libringbuffer/getcpu.h
new file mode 100644 (file)
index 0000000..f5f2f67
--- /dev/null
+++ b/libringbuffer/getcpu.h
@@ -0,0 +1,57 @@
+#ifndef _LTTNG_GETCPU_H
+#define _LTTNG_GETCPU_H
+
+/*
+ * Copyright (c) 2011 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; only
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#define _GNU_SOURCE
+#include <urcu/compiler.h>
+#include <sched.h>
+
+#ifdef UST_VALGRIND
+
+/*
+ * Fallback on cpu 0 if liblttng-ust is build with Valgrind support.
+ * get_cpu() returns the current CPU number. It may change due to
+ * migration, so it is only statistically accurate.
+ */
+static inline
+int lttng_ust_get_cpu(void)
+{
+       return 0;
+}
+
+#else
+
+/*
+ * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
+ */
+static inline
+int lttng_ust_get_cpu(void)
+{
+       int cpu;
+
+       cpu = sched_getcpu();
+       if (caa_unlikely(cpu < 0))
+               return 0;
+       return cpu;
+}
+
+#endif
+
+#endif /* _LTTNG_GETCPU_H */