[PATCH v6 4/4] perf lock: Report owner stack in usermode

[Chun-Tse Shao <ctshao@google.com>]

This patch parses `owner_lock_stat` into a RB tree, enabling ordered
reporting of owner lock statistics with stack traces. It also updates
the documentation for the `-o` option in contention mode, decouples `-o`
from `-t`, and issues a warning to inform users about the new behavior
of `-ov`.

Example output:
  $ sudo ~/linux/tools/perf/perf lock con -abvo -Y mutex-spin -E3 perf bench sched pipe
  ...
   contended   total wait     max wait     avg wait         type   caller

         171      1.55 ms     20.26 us      9.06 us        mutex   pipe_read+0x57
                          0xffffffffac6318e7  pipe_read+0x57
                          0xffffffffac623862  vfs_read+0x332
                          0xffffffffac62434b  ksys_read+0xbb
                          0xfffffffface604b2  do_syscall_64+0x82
                          0xffffffffad00012f  entry_SYSCALL_64_after_hwframe+0x76
          36    193.71 us     15.27 us      5.38 us        mutex   pipe_write+0x50
                          0xffffffffac631ee0  pipe_write+0x50
                          0xffffffffac6241db  vfs_write+0x3bb
                          0xffffffffac6244ab  ksys_write+0xbb
                          0xfffffffface604b2  do_syscall_64+0x82
                          0xffffffffad00012f  entry_SYSCALL_64_after_hwframe+0x76
           4     51.22 us     16.47 us     12.80 us        mutex   do_epoll_wait+0x24d
                          0xffffffffac691f0d  do_epoll_wait+0x24d
                          0xffffffffac69249b  do_epoll_pwait.part.0+0xb
                          0xffffffffac693ba5  __x64_sys_epoll_pwait+0x95
                          0xfffffffface604b2  do_syscall_64+0x82
                          0xffffffffad00012f  entry_SYSCALL_64_after_hwframe+0x76

  === owner stack trace ===

           3     31.24 us     15.27 us     10.41 us        mutex   pipe_read+0x348
                          0xffffffffac631bd8  pipe_read+0x348
                          0xffffffffac623862  vfs_read+0x332
                          0xffffffffac62434b  ksys_read+0xbb
                          0xfffffffface604b2  do_syscall_64+0x82
                          0xffffffffad00012f  entry_SYSCALL_64_after_hwframe+0x76
  ...

Signed-off-by: Chun-Tse Shao <ctshao@google.com>
---
 tools/perf/Documentation/perf-lock.txt |  6 +--
 tools/perf/builtin-lock.c              | 22 +++++++++-
 tools/perf/util/bpf_lock_contention.c  | 58 ++++++++++++++++++++++++++
 tools/perf/util/lock-contention.h      |  7 ++++
 4 files changed, 88 insertions(+), 5 deletions(-)

diff --git a/tools/perf/Documentation/perf-lock.txt b/tools/perf/Documentation/perf-lock.txt
index d3793054f7d3..255e4f3e9d2b 100644
--- a/tools/perf/Documentation/perf-lock.txt
+++ b/tools/perf/Documentation/perf-lock.txt
@@ -140,7 +140,6 @@ CONTENTION OPTIONS
 --use-bpf::
 	Use BPF program to collect lock contention stats instead of
 	using the input data.
-
 -a::
 --all-cpus::
         System-wide collection from all CPUs.
@@ -179,8 +178,9 @@ CONTENTION OPTIONS
 
 -o::
 --lock-owner::
-	Show lock contention stat by owners.  Implies --threads and
-	requires --use-bpf.
+	Show lock contention stat by owners. This option can be combined with -t,
+	which shows owner's per thread lock stats, or -v, which shows owner's
+	stacktrace. Requires --use-bpf.
 
 -Y::
 --type-filter=<value>::
diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
index 9bebc186286f..34cffa3c7cad 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -1817,6 +1817,22 @@ static void print_contention_result(struct lock_contention *con)
 			break;
 	}
 
+	if (con->owner && con->save_callstack && verbose > 0) {
+		struct rb_root root = RB_ROOT;
+
+		if (symbol_conf.field_sep)
+			fprintf(lock_output, "# owner stack trace:\n");
+		else
+			fprintf(lock_output, "\n=== owner stack trace ===\n\n");
+		while ((st = pop_owner_stack_trace(con)))
+			insert_to(&root, st, compare);
+
+		while ((st = pop_from(&root))) {
+			print_lock_stat(con, st);
+			zfree(st);
+		}
+	}
+
 	if (print_nr_entries) {
 		/* update the total/bad stats */
 		while ((st = pop_from_result())) {
@@ -1962,8 +1978,10 @@ static int check_lock_contention_options(const struct option *options,
 		}
 	}
 
-	if (show_lock_owner)
-		show_thread_stats = true;
+	if (show_lock_owner && !show_thread_stats) {
+		pr_warning("Now -o try to show owner's callstack instead of pid and comm.\n");
+		pr_warning("Please use -t option too to keep the old behavior.\n");
+	}
 
 	return 0;
 }
diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index 76542b86e83f..226ec7a06ab1 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -549,6 +549,64 @@ static const char *lock_contention_get_name(struct lock_contention *con,
 	return name_buf;
 }
 
+struct lock_stat *pop_owner_stack_trace(struct lock_contention *con)
+{
+	int stacks_fd, stat_fd;
+	u64 *stack_trace = NULL;
+	s32 stack_id;
+	struct contention_key ckey = {};
+	struct contention_data cdata = {};
+	size_t stack_size = con->max_stack * sizeof(*stack_trace);
+	struct lock_stat *st = NULL;
+
+	stacks_fd = bpf_map__fd(skel->maps.owner_stacks);
+	stat_fd = bpf_map__fd(skel->maps.owner_stat);
+	if (!stacks_fd || !stat_fd)
+		goto out_err;
+
+	stack_trace = zalloc(stack_size);
+	if (stack_trace == NULL)
+		goto out_err;
+
+	if (bpf_map_get_next_key(stacks_fd, NULL, stack_trace))
+		goto out_err;
+
+	bpf_map_lookup_elem(stacks_fd, stack_trace, &stack_id);
+	ckey.stack_id = stack_id;
+	bpf_map_lookup_elem(stat_fd, &ckey, &cdata);
+
+	st = zalloc(sizeof(struct lock_stat));
+	if (!st)
+		goto out_err;
+
+	st->name = strdup(stack_trace[0] ? lock_contention_get_name(con, NULL, stack_trace, 0) :
+					   "unknown");
+	if (!st->name)
+		goto out_err;
+
+	st->flags = cdata.flags;
+	st->nr_contended = cdata.count;
+	st->wait_time_total = cdata.total_time;
+	st->wait_time_max = cdata.max_time;
+	st->wait_time_min = cdata.min_time;
+	st->callstack = stack_trace;
+
+	if (cdata.count)
+		st->avg_wait_time = cdata.total_time / cdata.count;
+
+	bpf_map_delete_elem(stacks_fd, stack_trace);
+	bpf_map_delete_elem(stat_fd, &ckey);
+
+	return st;
+
+out_err:
+	if (stack_trace)
+		free(stack_trace);
+	if (st)
+		free(st);
+	return NULL;
+}
+
 int lock_contention_read(struct lock_contention *con)
 {
 	int fd, stack, err = 0;
diff --git a/tools/perf/util/lock-contention.h b/tools/perf/util/lock-contention.h
index a09f7fe877df..97fd33c57f17 100644
--- a/tools/perf/util/lock-contention.h
+++ b/tools/perf/util/lock-contention.h
@@ -168,6 +168,8 @@ int lock_contention_stop(void);
 int lock_contention_read(struct lock_contention *con);
 int lock_contention_finish(struct lock_contention *con);
 
+struct lock_stat *pop_owner_stack_trace(struct lock_contention *con);
+
 #else  /* !HAVE_BPF_SKEL */
 
 static inline int lock_contention_prepare(struct lock_contention *con __maybe_unused)
@@ -187,6 +189,11 @@ static inline int lock_contention_read(struct lock_contention *con __maybe_unuse
 	return 0;
 }
 
+struct lock_stat *pop_owner_stack_trace(struct lock_contention *con)
+{
+	return NULL;
+}
+
 #endif  /* HAVE_BPF_SKEL */
 
 #endif  /* PERF_LOCK_CONTENTION_H */
-- 
2.48.1.601.g30ceb7b040-goog