tracing/fastboot: Enable boot tracing only during initcalls

Impact: modify boot tracer

We used to disable the initcall tracing at a specified time (IE: end
of builtin initcalls). But we don't need it anymore. It will be
stopped when initcalls are finished.

However we want two things:

_Start this tracing only after pre-smp initcalls are finished.

_Since we are planning to trace sched_switches at the same time, we
want to enable them only during the initcall execution.

For this purpose, this patch introduce two functions to enable/disable
the sched_switch tracing during boot.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 22 insertions, 2 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index e46a7b34037c..4642959e5bda 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -234,6 +234,11 @@ ftrace_init_module(unsigned long *start, unsigned long *end) { }
 #endif
 
 
+/*
+ * Structure which defines the trace of an initcall.
+ * You don't have to fill the func field since it is
+ * only used internally by the tracer.
+ */
 struct boot_trace {
         pid_t                   caller;
         char                    func[KSYM_NAME_LEN];
@@ -244,13 +249,28 @@ struct boot_trace {
 };
 
 #ifdef CONFIG_BOOT_TRACER
+/* Append the trace on the ring-buffer */
 extern void trace_boot(struct boot_trace *it, initcall_t fn);
+
+/* Tells the tracer that smp_pre_initcall is finished.
+ * So we can start the tracing
+ */
 extern void start_boot_trace(void);
-extern void stop_boot_trace(void);
+
+/* Resume the tracing of other necessary events
+ * such as sched switches
+ */
+extern void enable_boot_trace(void);
+
+/* Suspend this tracing. Actually, only sched_switches tracing have
+ * to be suspended. Initcalls doesn't need it.)
+ */
+extern void disable_boot_trace(void);
 #else
 static inline void trace_boot(struct boot_trace *it, initcall_t fn) { }
 static inline void start_boot_trace(void) { }
-static inline void stop_boot_trace(void) { }
+static inline void enable_boot_trace(void) { }
+static inline void disable_boot_trace(void) { }
 #endif