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

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Date:   Thu, 30 Nov 2023 10:29:30 -0800
From:   Ian Rogers <irogers@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>
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>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        "Steinar H. Gunderson" <sesse@...gle.com>,
        Liam Howlett <liam.howlett@...cle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Colin Ian King <colin.i.king@...il.com>,
        Dmitrii Dolgov <9erthalion6@...il.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        Ming Wang <wangming01@...ngson.cn>,
        James Clark <james.clark@....com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Leo Yan <leo.yan@...aro.org>,
        Ravi Bangoria <ravi.bangoria@....com>,
        German Gomez <german.gomez@....com>,
        Changbin Du <changbin.du@...wei.com>,
        Paolo Bonzini <pbonzini@...hat.com>, Li Dong <lidong@...o.com>,
        Sandipan Das <sandipan.das@....com>,
        liuwenyu <liuwenyu7@...wei.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Guilherme Amadio <amadio@...too.org>
Subject: Re: [PATCH v5 08/50] perf record: Be lazier in allocating lost
 samples buffer

On Wed, Nov 29, 2023 at 6:09 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Mon, Nov 27, 2023 at 2:09 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);
>
> To minimize the allocation size, this can be
> sizeof(*lost) + session->machines.host.id_hdr_size
> instead of PERF_SAMPLE_MAX_SIZE.

Sounds good, should probably be a follow up. The current size is
PERF_SAMPLE_MAX_SIZE.

Thanks,
Ian

> 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
> >