In most configurations, it works well with skipping 4 entries by
default. If some systems still have 3 BPF internal stack frames,
the next frame should be in a lock function which will be skipped
later when it tries to find a caller. So increasing to 4 won't
affect such systems too.
With --stack-skip=0, I can see something like this:
24 49.84 us 7.41 us 2.08 us mutex bpf_prog_e1b85959d520446c_contention_begin+0x12e
0xffffffffc045040e bpf_prog_e1b85959d520446c_contention_begin+0x12e
0xffffffffc045040e bpf_prog_e1b85959d520446c_contention_begin+0x12e
0xffffffff82ea2071 bpf_trace_run2+0x51
0xffffffff82de775b __bpf_trace_contention_begin+0xb
0xffffffff82c02045 __mutex_lock+0x245
0xffffffff82c019e3 __mutex_lock_slowpath+0x13
0xffffffff82c019c0 mutex_lock+0x20
0xffffffff830a083c kernfs_iop_permission+0x2c
Cc: Song Liu <song@xxxxxxxxxx>
Cc: bpf@xxxxxxxxxxxxxxx
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
tools/perf/util/lock-contention.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/perf/util/lock-contention.h b/tools/perf/util/lock-contention.h
index b8cb8830b7bc..e3c061b1795b 100644
--- a/tools/perf/util/lock-contention.h
+++ b/tools/perf/util/lock-contention.h
@@ -91,7 +91,7 @@ struct thread_stat {
* Number of stack trace entries to skip when finding callers.
* The first few entries belong to the locking implementation itself.
*/
-#define CONTENTION_STACK_SKIP 3
+#define CONTENTION_STACK_SKIP 4
/*
* flags for lock:contention_begin
--
2.38.1.273.g43a17bfeac-goog
