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

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Message-ID: <Y/Sw7RurDK/fq02m@krava>
Date:   Tue, 21 Feb 2023 12:54:21 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Song Liu <song@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Leo Yan <leo.yan@...aro.org>,
        James Clark <james.clark@....com>, Hao Luo <haoluo@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH 4/8] perf record: Record dropped sample count

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@...nel.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