perf thread: Add a knob for LBR stitch approach

The LBR stitch approach should be disabled by default. Because

- The stitching approach base on LBR call stack technology. The known
  limitations of LBR call stack technology still apply to the approach,
  e.g. Exception handing such as setjmp/longjmp will have calls/returns
  not match.

- This approach is not foolproof. There can be cases where it creates
  incorrect call stacks from incorrect matches. There is no attempt to
  validate any matches in another way.

The 'lbr_stitch_enable' is used to indicate whether enable LBR stitch
approach, which is disabled by default. The following patch will
introduce a new option for each tools to enable the LBR stitch
approach.

Signed-off-by: Kan Liang <[email protected]>
Reviewed-by: Andi Kleen <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexey Budankov <[email protected]>
Cc: Mathieu Poirier <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Pavel Gerasimov <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi Bangoria <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Vitaly Slobodskoy <[email protected]>
Link: http://lore.kernel.org/lkml/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

Author: Kan Liang

tools/perf/util/thread.c

@@ -47,6 +47,7 @@ struct thread *thread__new(pid_t pid, pid_t tid)
 		thread->tid = tid;
 		thread->ppid = -1;
 		thread->cpu = -1;
+		thread->lbr_stitch_enable = false;
 		INIT_LIST_HEAD(&thread->namespaces_list);
 		INIT_LIST_HEAD(&thread->comm_list);
 		init_rwsem(&thread->namespaces_lock);

tools/perf/util/thread.h

@@ -46,6 +46,9 @@ struct thread {
 	struct srccode_state	srccode_state;
 	bool			filter;
 	int			filter_entry_depth;
+
+	/* LBR call stack stitch */
+	bool			lbr_stitch_enable;
 };
 
 struct machine;