Re: [PATCH v5 4/5] perf lock: Report owner stack in usermode

Namhyung Kim
2025-02-13T23:24:17Z

On Wed, Feb 12, 2025 at 02:24:55PM -0800, Chun-Tse Shao wrote:
> Parse `owner_lock_stat` into a rb tree, and report owner lock stats with
> stack trace in order.
>
> 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/builtin-lock.c | 19 ++++++++--
> tools/perf/util/bpf_lock_contention.c | 54 +++++++++++++++++++++++++++
> tools/perf/util/lock-contention.h | 7 ++++
> 3 files changed, 77 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
> index 9bebc186286f..3dc100cf30ef 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) {
> + 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())) {
> @@ -1962,9 +1978,6 @@ static int check_lock_contention_options(const struct option *options,
> }
> }
>
> - if (show_lock_owner)
> - show_thread_stats = true;
> -
> return 0;
> }
>
> diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
> index 76542b86e83f..dc83b02c9724 100644
> --- a/tools/perf/util/bpf_lock_contention.c
> +++ b/tools/perf/util/bpf_lock_contention.c
> @@ -549,6 +549,60 @@ 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;
> + 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;
> + char name[KSYM_NAME_LEN];
> +
> + stacks_fd = bpf_map__fd(skel->maps.owner_stacks);
> + stat_fd = bpf_map__fd(skel->maps.owner_stat);
> + if (!stacks_fd || !stat_fd)
> + return NULL;
> +
> + stack_trace = zalloc(stack_size);
> + if (stack_trace == NULL)
> + return NULL;
> +
> + if (bpf_map_get_next_key(stacks_fd, NULL, stack_trace))
> + return NULL;

Please free(stack_trace).

> +
> + 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)
> + return NULL;

And here too.

> +
> + strcpy(name,
> + stack_trace[0] ? lock_contention_get_name(con, NULL, stack_trace, 0) : "unknown");
> +
> + st->name = strdup(name);
> + if (!st->name)
> + return NULL;

Why not

if (stack_trace[0])
st->name = strdup(lock_contention_get_name(con, NULL, stack_trace, 0));
else
st->name = strdup("unknown");

if (st->name == NULL) {
free(stack_trace);
free(st);
return NULL;
}

? I don't think you need the name[].

Thanks,
Namhyung

> +
> + 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;
> +}
> +
> 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 */
> --
> 2.48.1.502.g6dc24dfdaf-goog
>