Merge branch 'bpf: Add missed stats for kprobes'

Jiri Olsa says:

====================
hi,
at the moment we can't retrieve the number of missed kprobe
executions and subsequent execution of BPF programs.

This patchset adds:
  - counting of missed execution on attach layer for:
    . kprobes attached through perf link (kprobe/ftrace)
    . kprobes attached through kprobe.multi link (fprobe)
  - counting of recursion_misses for BPF kprobe programs

It's still technically possible to create kprobe without perf link (using
SET_BPF perf ioctl) in which case we don't have a way to retrieve the kprobe's
'missed' count. However both libbpf and cilium/ebpf libraries use perf link
if it's available, and for old kernels without perf link support we can use
BPF program to retrieve the kprobe missed count.

v3 changes:
  - added acks [Song]
  - make test_missed not serial [Andrii]

Also available at:
  https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
  bpf/missed_stats

thanks,
jirka
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
index 2e5c231e08ac..4b1407b05056 100644
--- a/tools/bpf/bpftool/link.c
+++ b/tools/bpf/bpftool/link.c
@@ -265,6 +265,7 @@ show_kprobe_multi_json(struct bpf_link_info *info, json_writer_t *wtr)
 	jsonw_bool_field(json_wtr, "retprobe",
 			 info->kprobe_multi.flags & BPF_F_KPROBE_MULTI_RETURN);
 	jsonw_uint_field(json_wtr, "func_cnt", info->kprobe_multi.count);
+	jsonw_uint_field(json_wtr, "missed", info->kprobe_multi.missed);
 	jsonw_name(json_wtr, "funcs");
 	jsonw_start_array(json_wtr);
 	addrs = u64_to_ptr(info->kprobe_multi.addrs);
@@ -301,6 +302,7 @@ show_perf_event_kprobe_json(struct bpf_link_info *info, json_writer_t *wtr)
 	jsonw_string_field(wtr, "func",
 			   u64_to_ptr(info->perf_event.kprobe.func_name));
 	jsonw_uint_field(wtr, "offset", info->perf_event.kprobe.offset);
+	jsonw_uint_field(wtr, "missed", info->perf_event.kprobe.missed);
 }
 
 static void
@@ -641,6 +643,8 @@ static void show_kprobe_multi_plain(struct bpf_link_info *info)
 	else
 		printf("\n\tkprobe.multi  ");
 	printf("func_cnt %u  ", info->kprobe_multi.count);
+	if (info->kprobe_multi.missed)
+		printf("missed %llu  ", info->kprobe_multi.missed);
 	addrs = (__u64 *)u64_to_ptr(info->kprobe_multi.addrs);
 	qsort(addrs, info->kprobe_multi.count, sizeof(__u64), cmp_u64);
 
@@ -683,6 +687,8 @@ static void show_perf_event_kprobe_plain(struct bpf_link_info *info)
 	printf("%s", buf);
 	if (info->perf_event.kprobe.offset)
 		printf("+%#x", info->perf_event.kprobe.offset);
+	if (info->perf_event.kprobe.missed)
+		printf("  missed %llu", info->perf_event.kprobe.missed);
 	printf("  ");
 }