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

From: Namhyung Kim
Date: Wed Nov 29 2023 - 21:09:59 EST


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
>