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

Jiri Olsa
2023-02-21T11:54:31Z

On Sat, Feb 18, 2023 at 10:13:25PM -0800, Namhyung Kim wrote:
> 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;

SNIP

> @@ -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);

ah that's why I did not see this in kernel code, it's set by record, nice ;-)

jirka