linux-kernel - Re: [PATCH v3 20/50] perf record: Be lazier in allocating lost samples buffer

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Date:   Wed, 25 Oct 2023 12:00:56 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Nick Terrell <terrelln@...com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>, Leo Yan <leo.yan@...aro.org>,
        Song Liu <song@...nel.org>,
        Sandipan Das <sandipan.das@....com>,
        James Clark <james.clark@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Liam Howlett <liam.howlett@...cle.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Ravi Bangoria <ravi.bangoria@....com>,
        German Gomez <german.gomez@....com>,
        Changbin Du <changbin.du@...wei.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        liuwenyu <liuwenyu7@...wei.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v3 20/50] perf record: Be lazier in allocating lost
 samples buffer

On Tue, Oct 24, 2023 at 3:25 PM Ian Rogers <irogers@...gle.com> wrote:
>
> Wait until a lost sample occurs to allocate the lost samples buffer,
> often the buffer isn't necessary. This saves a 64kb allocation and
> 5.3kb of peak memory consumption.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/builtin-record.c | 29 +++++++++++++++++++----------
>  1 file changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 9b4f3805ca92..b6c8c1371b39 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1924,21 +1924,13 @@ static void __record__save_lost_samples(struct record *rec, struct evsel *evsel,
>  static void record__read_lost_samples(struct record *rec)
>  {
>         struct perf_session *session = rec->session;
> -       struct perf_record_lost_samples *lost;
> +       struct perf_record_lost_samples *lost = NULL;
>         struct evsel *evsel;
>
>         /* there was an error during record__open */
>         if (session->evlist == NULL)
>                 return;
>
> -       lost = zalloc(PERF_SAMPLE_MAX_SIZE);

Sorry for naively choosing the max size. :-p
It could be sizeof(*lost) + machine->id_hdr_size.

Thanks,
Namhyung


> -       if (lost == NULL) {
> -               pr_debug("Memory allocation failed\n");
> -               return;
> -       }
> -
> -       lost->header.type = PERF_RECORD_LOST_SAMPLES;
> -
>         evlist__for_each_entry(session->evlist, evsel) {
>                 struct xyarray *xy = evsel->core.sample_id;
>                 u64 lost_count;
> @@ -1961,6 +1953,14 @@ static void record__read_lost_samples(struct record *rec)
>                                 }
>
>                                 if (count.lost) {
> +                                       if (!lost) {
> +                                               lost = zalloc(PERF_SAMPLE_MAX_SIZE);
> +                                               if (!lost) {
> +                                                       pr_debug("Memory allocation failed\n");
> +                                                       return;
> +                                               }
> +                                               lost->header.type = PERF_RECORD_LOST_SAMPLES;
> +                                       }
>                                         __record__save_lost_samples(rec, evsel, lost,
>                                                                     x, y, count.lost, 0);
>                                 }
> @@ -1968,9 +1968,18 @@ static void record__read_lost_samples(struct record *rec)
>                 }
>
>                 lost_count = perf_bpf_filter__lost_count(evsel);
> -               if (lost_count)
> +               if (lost_count) {
> +                       if (!lost) {
> +                               lost = zalloc(PERF_SAMPLE_MAX_SIZE);
> +                               if (!lost) {
> +                                       pr_debug("Memory allocation failed\n");
> +                                       return;
> +                               }
> +                               lost->header.type = PERF_RECORD_LOST_SAMPLES;
> +                       }
>                         __record__save_lost_samples(rec, evsel, lost, 0, 0, lost_count,
>                                                     PERF_RECORD_MISC_LOST_SAMPLES_BPF);
> +               }
>         }
>  out:
>         free(lost);
> --
> 2.42.0.758.gaed0368e0e-goog
>