[tip: perf/core] perf thread: Add a knob for LBR stitch approach

[tip-bot2 for Kan Liang]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     771fd155dfaa5332da69d606db16fe27bd9d388d
Gitweb:        https://git.kernel.org/tip/771fd155dfaa5332da69d606db16fe27bd9d388d
Author:        Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
AuthorDate:    Thu, 19 Mar 2020 13:25:09 -07:00
Committer:     Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitterDate: Sat, 18 Apr 2020 09:05:01 -03:00

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 <kan.liang@xxxxxxxxxxxxxxx>
Reviewed-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Pavel Gerasimov <pavel.gerasimov@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Vitaly Slobodskoy <vitaly.slobodskoy@xxxxxxxxx>
Link: http://lore.kernel.org/lkml/20200319202517.23423-10-kan.liang@xxxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/thread.c | 1 +
 tools/perf/util/thread.h | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index 28b7193..1f080db 100644
--- a/tools/perf/util/thread.c
+++ b/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);
diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
index 20b96b5..9529405 100644
--- a/tools/perf/util/thread.h
+++ b/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;