Ring buffer: use shmp (shared-memory pointers) for per-channel shm structures

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

diff --git a/libringbuffer/smp.h b/libringbuffer/smp.h
new file mode 100644 (file)
index 0000000..3d138a9
--- /dev/null
+++ b/libringbuffer/smp.h
@@ -0,0 +1,73 @@
+#ifndef _LIBRINGBUFFER_SMP_H
+#define _LIBRINGBUFFER_SMP_H
+
+/*
+ * libringbuffer/smp.h
+ *
+ * Copyright 2011 (c) - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * Dual LGPL v2.1/GPL v2 license.
+ */
+
+#include <ust/core.h>
+
+/*
+ * 4kB of per-cpu data available. Enough to hold the control structures,
+ * but not ring buffers.
+ */
+#define PER_CPU_MEM_SIZE       4096
+
+extern int __num_possible_cpus;
+extern void _get_num_possible_cpus(void);
+
+static inline
+int num_possible_cpus(void)
+{
+       if (!__num_possible_cpus)
+               _get_num_possible_cpus();
+       return __num_possible_cpus;
+}
+
+/*
+ * get_cpu() returns the current CPU number. It may change due to
+ * migration, so it is only statistically accurate.
+ */
+#ifndef UST_VALGRIND
+static inline
+int get_cpu(void)
+{
+       int cpu;
+
+       cpu = sched_getcpu();
+       if (likely(cpu >= 0))
+               return cpu;
+       /*
+        * If getcpu(2) is not implemented in the Kernel use CPU 0 as fallback.
+        */
+       return 0;
+}
+
+#else  /* #else #ifndef UST_VALGRIND */
+static inline
+int get_cpu(void)
+{
+       /*
+        * Valgrind does not support the sched_getcpu() vsyscall.
+        * It causes it to detect a segfault in the program and stop it.
+        * So if we want to check libust with valgrind, we have to refrain
+        * from using this call. TODO: it would probably be better to return
+        * other values too, to better test it.
+        */
+       return 0;
+}
+#endif /* #else #ifndef UST_VALGRIND */
+
+static inline
+void put_cpu(void)
+{
+}
+
+#define for_each_possible_cpu(cpu)             \
+       for ((cpu) = 0; (cpu) < num_possible_cpus(); (cpu)++)
+
+#endif /* _LIBRINGBUFFER_SMP_H */