perf/core: Set event's default ::overflow_handler()

Set a default event->overflow_handler in perf_event_alloc() so don't
need to check event->overflow_handler in __perf_event_overflow().
Following commits can give a different default overflow_handler.

Initial idea comes from Peter:

  http://lkml.kernel.org/r/[email protected]

Since the default value of event->overflow_handler is not NULL, existing
'if (!overflow_handler)' checks need to be changed.

is_default_overflow_handler() is introduced for this.

No extra performance overhead is introduced into the hot path because in the
original code we still need to read this handler from memory. A conditional
branch is avoided so actually we remove some instructions.

Signed-off-by: Wang Nan <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Brendan Gregg <[email protected]>
Cc: He Kuang <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vince Weaver <[email protected]>
Cc: Zefan Li <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

1 files changed, 6 insertions, 0 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 15588d4c581d..4065ca2d7149 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -838,6 +838,12 @@ extern void perf_event_output(struct perf_event *event,
 				struct perf_sample_data *data,
 				struct pt_regs *regs);
 
+static inline bool
+is_default_overflow_handler(struct perf_event *event)
+{
+	return (event->overflow_handler == perf_event_output);
+}
+
 extern void
 perf_event_header__init_id(struct perf_event_header *header,
 			   struct perf_sample_data *data,