Move the getcpu plugin implementation to liblttn-ust-common

[lttng-ust.git] / src / common / getcpu.h

diff --git a/src/common/getcpu.h b/src/common/getcpu.h
new file mode 100644 (file)
index 0000000..3bf9076
--- /dev/null
+++ b/src/common/getcpu.h
@@ -0,0 +1,115 @@
+/*
+ * SPDX-License-Identifier: LGPL-2.1-only
+ *
+ * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ */
+
+#ifndef _UST_COMMON_GETCPU_H
+#define _UST_COMMON_GETCPU_H
+
+#include <urcu/compiler.h>
+#include <urcu/system.h>
+#include <urcu/arch.h>
+
+#include <lttng/ust-getcpu.h>
+
+/*
+ * Function pointer to the user provided getcpu callback, can be set at library
+ * initialization by a dlopened plugin or at runtime by a user by calling
+ * lttng_ust_getcpu_override() from the public API.
+ *
+ * This is an ABI symbol of liblttng-ust-common accessed by other libraries
+ * through the static inline function in this file. It is initialised in the
+ * liblttng-ust-common constructor.
+ */
+extern int (*lttng_ust_get_cpu_sym)(void);
+
+#ifdef LTTNG_UST_DEBUG_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_internal(void)
+{
+       return 0;
+}
+
+#else
+
+/*
+ * sched_getcpu.
+ */
+#ifdef __linux__
+
+#if !HAVE_SCHED_GETCPU
+#include <sys/syscall.h>
+#define __getcpu(cpu, node, cache)     syscall(__NR_getcpu, cpu, node, cache)
+/*
+ * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
+ */
+static inline
+int lttng_ust_get_cpu_internal(void)
+{
+       int cpu, ret;
+
+       ret = __getcpu(&cpu, NULL, NULL);
+       if (caa_unlikely(ret < 0))
+               return 0;
+       return cpu;
+}
+#else /* HAVE_SCHED_GETCPU */
+#include <sched.h>
+
+/*
+ * If getcpu is not implemented in the kernel, use cpu 0 as fallback.
+ */
+static inline
+int lttng_ust_get_cpu_internal(void)
+{
+       int cpu;
+
+       cpu = sched_getcpu();
+       if (caa_unlikely(cpu < 0))
+               return 0;
+       return cpu;
+}
+#endif /* HAVE_SCHED_GETCPU */
+
+#elif (defined(__FreeBSD__) || defined(__CYGWIN__))
+
+/*
+ * FreeBSD and Cygwin do not allow query of CPU ID. Always use CPU
+ * number 0, with the assocated performance degradation on SMP.
+ */
+static inline
+int lttng_ust_get_cpu_internal(void)
+{
+       return 0;
+}
+
+#else
+#error "Please add support for your OS into liblttng-ust/compat.h."
+#endif
+
+#endif
+
+static inline
+int lttng_ust_get_cpu(void)
+{
+       int (*lttng_ust_get_cpu_current)(void) = CMM_LOAD_SHARED(lttng_ust_get_cpu_sym);
+
+       /*
+        * Fallback to the internal getcpu implementation if no override was
+        * provided the user.
+        */
+       if (caa_likely(!lttng_ust_get_cpu_current)) {
+               return lttng_ust_get_cpu_internal();
+       } else {
+               return lttng_ust_get_cpu_current();
+       }
+}
+
+#endif /* _LTTNG_GETCPU_H */