[PATCH 4/8] perf record: Record dropped sample count

Namhyung Kim
2023-02-19T06:13:48Z

When it uses bpf filters, event might drop some samples. It'd be nice
if it can report how many samples it lost. As LOST_SAMPLES event can
carry the similar information, let's use it for bpf filters.

To indicate it's from BPF filters, add a new misc flag for that and
do not display cpu load warnings.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/lib/perf/include/perf/event.h | 2 ++
tools/perf/builtin-record.c | 37 ++++++++++++++++++-----------
tools/perf/util/bpf-filter.c | 7 ++++++
tools/perf/util/bpf-filter.h | 5 ++++
tools/perf/util/session.c | 3 ++-
5 files changed, 39 insertions(+), 15 deletions(-)

diff --git a/tools/lib/perf/include/perf/event.h b/tools/lib/perf/include/perf/event.h
index ad47d7b31046..51b9338f4c11 100644
--- a/tools/lib/perf/include/perf/event.h
+++ b/tools/lib/perf/include/perf/event.h
@@ -70,6 +70,8 @@ struct perf_record_lost {
__u64 lost;
};

+#define PERF_RECORD_MISC_LOST_SAMPLES_BPF (1 << 15)
+
struct perf_record_lost_samples {
struct perf_event_header header;
__u64 lost;
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 6429915d376d..d4037308209c 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1865,24 +1865,16 @@ record__switch_output(struct record *rec, bool at_exit)
return fd;
}

-static void __record__read_lost_samples(struct record *rec, struct evsel *evsel,
+static void __record__save_lost_samples(struct record *rec, struct evsel *evsel,
struct perf_record_lost_samples *lost,
- int cpu_idx, int thread_idx)
+ int cpu_idx, int thread_idx, u64 lost_count,
+ u16 misc_flag)
{
- struct perf_counts_values count;
struct perf_sample_id *sid;
struct perf_sample sample = {};
int id_hdr_size;

- if (perf_evsel__read(&evsel->core, cpu_idx, thread_idx, &count) < 0) {
- pr_err("read LOST count failed\n");
- return;
- }
-
- if (count.lost == 0)
- return;
-
- lost->lost = count.lost;
+ lost->lost = lost_count;
if (evsel->core.ids) {
sid = xyarray__entry(evsel->core.sample_id, cpu_idx, thread_idx);
sample.id = sid->id;
@@ -1891,6 +1883,7 @@ static void __record__read_lost_samples(struct record *rec, struct evsel *evsel,
id_hdr_size = perf_event__synthesize_id_sample((void *)(lost + 1),
evsel->core.attr.sample_type, &sample);
lost->header.size = sizeof(*lost) + id_hdr_size;
+ lost->header.misc = misc_flag;
record__write(rec, NULL, lost, lost->header.size);
}

@@ -1914,6 +1907,7 @@ static void record__read_lost_samples(struct record *rec)

evlist__for_each_entry(session->evlist, evsel) {
struct xyarray *xy = evsel->core.sample_id;
+ u64 lost_count;

if (xy == NULL || evsel->core.fd == NULL)
continue;
@@ -1925,12 +1919,27 @@ static void record__read_lost_samples(struct record *rec)

for (int x = 0; x < xyarray__max_x(xy); x++) {
for (int y = 0; y < xyarray__max_y(xy); y++) {
- __record__read_lost_samples(rec, evsel, lost, x, y);
+ struct perf_counts_values count;
+
+ if (perf_evsel__read(&evsel->core, x, y, &count) < 0) {
+ pr_err("read LOST count failed\n");
+ goto out;
+ }
+
+ if (count.lost) {
+ __record__save_lost_samples(rec, evsel, lost,
+ x, y, count.lost, 0);
+ }
}
}
+
+ lost_count = perf_bpf_filter__lost_count(evsel);
+ if (lost_count)
+ __record__save_lost_samples(rec, evsel, lost, 0, 0, lost_count,
+ PERF_RECORD_MISC_LOST_SAMPLES_BPF);
}
+out:
free(lost);
-
}

static volatile sig_atomic_t workload_exec_errno;
diff --git a/tools/perf/util/bpf-filter.c b/tools/perf/util/bpf-filter.c
index f47420cf81c9..11fb391c92e9 100644
--- a/tools/perf/util/bpf-filter.c
+++ b/tools/perf/util/bpf-filter.c
@@ -76,6 +76,13 @@ int perf_bpf_filter__destroy(struct evsel *evsel)
return 0;
}

+u64 perf_bpf_filter__lost_count(struct evsel *evsel)
+{
+ struct sample_filter_bpf *skel = evsel->bpf_skel;
+
+ return skel ? skel->bss->dropped : 0;
+}
+
struct perf_bpf_filter_expr *perf_bpf_filter_expr__new(unsigned long sample_flags,
enum perf_bpf_filter_op op,
unsigned long val)
diff --git a/tools/perf/util/bpf-filter.h b/tools/perf/util/bpf-filter.h
index 6077930073f9..36b44c8188ab 100644
--- a/tools/perf/util/bpf-filter.h
+++ b/tools/perf/util/bpf-filter.h
@@ -22,6 +22,7 @@ struct perf_bpf_filter_expr *perf_bpf_filter_expr__new(unsigned long sample_flag
int perf_bpf_filter__parse(struct list_head *expr_head, const char *str);
int perf_bpf_filter__prepare(struct evsel *evsel);
int perf_bpf_filter__destroy(struct evsel *evsel);
+u64 perf_bpf_filter__lost_count(struct evsel *evsel);

#else /* !HAVE_BPF_SKEL */

@@ -38,5 +39,9 @@ static inline int perf_bpf_filter__destroy(struct evsel *evsel)
{
return -ENOSYS;
}
+static inline u64 perf_bpf_filter__lost_count(struct evsel *evsel)
+{
+ return 0;
+}
#endif /* HAVE_BPF_SKEL*/
#endif /* PERF_UTIL_BPF_FILTER_H */
\ No newline at end of file
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 749d5b5c135b..7d8d057d1772 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1582,7 +1582,8 @@ static int machines__deliver_event(struct machines *machines,
evlist->stats.total_lost += event->lost.lost;
return tool->lost(tool, event, sample, machine);
case PERF_RECORD_LOST_SAMPLES:
- if (tool->lost_samples == perf_event__process_lost_samples)
+ if (tool->lost_samples == perf_event__process_lost_samples &&
+ !(event->header.misc & PERF_RECORD_MISC_LOST_SAMPLES_BPF))
evlist->stats.total_lost_samples += event->lost_samples.lost;
return tool->lost_samples(tool, event, sample, machine);
case PERF_RECORD_READ:
--
2.39.2.637.g21b0678d19-goog