Re: [PATCH v5 08/50] perf record: Be lazier in allocating lost samples buffer

[Namhyung Kim]

On Mon, Nov 27, 2023 at 2:09 PM Ian Rogers <irogers@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
>  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);

To minimize the allocation size, this can be
sizeof(*lost) + session->machines.host.id_hdr_size
instead of PERF_SAMPLE_MAX_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);
> --
> 2.43.0.rc1.413.gea7ed67945-goog
>