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

Adrian Hunter
2023-03-07T13:07:26Z

On 23/02/23 01:01, 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 | 38 ++++++++++++++++++-----------
> tools/perf/util/bpf-filter.c | 7 ++++++
> tools/perf/util/bpf-filter.h | 5 ++++
> tools/perf/util/session.c | 3 ++-
> 5 files changed, 40 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 8374117e66f6..197e802a150b 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -52,6 +52,7 @@
> #include "util/pmu-hybrid.h"
> #include "util/evlist-hybrid.h"
> #include "util/off_cpu.h"
> +#include "util/bpf-filter.h"
> #include "asm/bug.h"
> #include "perf.h"
> #include "cputopo.h"
> @@ -1856,24 +1857,16 @@ 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;
> @@ -1882,6 +1875,7 @@ 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);
> }
>
> @@ -1905,6 +1899,7 @@ 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;
> @@ -1916,12 +1911,27 @@ 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 e1b1a5343bad..660db5ccd3da 100644
> --- a/tools/perf/util/bpf-filter.c
> +++ b/tools/perf/util/bpf-filter.c
> @@ -69,6 +69,13 @@ 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)

Needs __maybe_unused on the parameters

> +{
> + 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);