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    SubjectRe: [PATCH] perf tools: Move probing cgroup sampling support
    On Thu, May 27, 2021 at 11:28:35AM -0700, Namhyung Kim wrote:
    > I found that checking cgroup sampling support using the missing
    > features doesn't work on old kernels. Because it added both
    > attr.cgroup bit and PERF_SAMPLE_CGROUP bit, it needs to check
    > whichever comes first (usually the actual event, not dummy).
    >
    > But it only checks the attr.cgroup bit which is set only in the dummy
    > event so cannot detect failtures due the sample bits. Also we don't
    > ignore the missing feature and retry, it'd be better checking it with
    > the API probing logic.
    >
    > Signed-off-by: Namhyung Kim <namhyung@kernel.org>

    Acked-by: Jiri Olsa <jolsa@redhat.com>

    thanks,
    jirka

    > ---
    > tools/perf/builtin-record.c | 6 ++++++
    > tools/perf/util/evsel.c | 6 +-----
    > tools/perf/util/evsel.h | 1 -
    > tools/perf/util/perf_api_probe.c | 10 ++++++++++
    > tools/perf/util/perf_api_probe.h | 1 +
    > 5 files changed, 18 insertions(+), 6 deletions(-)
    >
    > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
    > index bc3dd379eb67..71efe6573ee7 100644
    > --- a/tools/perf/builtin-record.c
    > +++ b/tools/perf/builtin-record.c
    > @@ -2733,6 +2733,12 @@ int cmd_record(int argc, const char **argv)
    > rec->no_buildid = true;
    > }
    >
    > + if (rec->opts.record_cgroup && !perf_can_record_cgroup()) {
    > + pr_err("Kernel has no cgroup sampling support.\n");
    > + err = -EINVAL;
    > + goto out_opts;
    > + }
    > +
    > if (rec->opts.kcore)
    > rec->data.is_dir = true;
    >
    > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
    > index 4a3cd1b5bb33..2462584d0ee5 100644
    > --- a/tools/perf/util/evsel.c
    > +++ b/tools/perf/util/evsel.c
    > @@ -1217,7 +1217,7 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
    > attr->namespaces = track;
    >
    > if (opts->record_cgroup) {
    > - attr->cgroup = track && !perf_missing_features.cgroup;
    > + attr->cgroup = track;
    > evsel__set_sample_bit(evsel, CGROUP);
    > }
    >
    > @@ -1933,10 +1933,6 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
    > perf_missing_features.data_page_size = true;
    > pr_debug2_peo("Kernel has no PERF_SAMPLE_DATA_PAGE_SIZE support, bailing out\n");
    > goto out_close;
    > - } else if (!perf_missing_features.cgroup && evsel->core.attr.cgroup) {
    > - perf_missing_features.cgroup = true;
    > - pr_debug2_peo("Kernel has no cgroup sampling support, bailing out\n");
    > - goto out_close;
    > } else if (!perf_missing_features.branch_hw_idx &&
    > (evsel->core.attr.branch_sample_type & PERF_SAMPLE_BRANCH_HW_INDEX)) {
    > perf_missing_features.branch_hw_idx = true;
    > diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
    > index 75cf5dbfe208..fecf13c0e4da 100644
    > --- a/tools/perf/util/evsel.h
    > +++ b/tools/perf/util/evsel.h
    > @@ -168,7 +168,6 @@ struct perf_missing_features {
    > bool bpf;
    > bool aux_output;
    > bool branch_hw_idx;
    > - bool cgroup;
    > bool data_page_size;
    > bool code_page_size;
    > bool weight_struct;
    > diff --git a/tools/perf/util/perf_api_probe.c b/tools/perf/util/perf_api_probe.c
    > index 829af17a0867..020411682a3c 100644
    > --- a/tools/perf/util/perf_api_probe.c
    > +++ b/tools/perf/util/perf_api_probe.c
    > @@ -103,6 +103,11 @@ static void perf_probe_build_id(struct evsel *evsel)
    > evsel->core.attr.build_id = 1;
    > }
    >
    > +static void perf_probe_cgroup(struct evsel *evsel)
    > +{
    > + evsel->core.attr.cgroup = 1;
    > +}
    > +
    > bool perf_can_sample_identifier(void)
    > {
    > return perf_probe_api(perf_probe_sample_identifier);
    > @@ -182,3 +187,8 @@ bool perf_can_record_build_id(void)
    > {
    > return perf_probe_api(perf_probe_build_id);
    > }
    > +
    > +bool perf_can_record_cgroup(void)
    > +{
    > + return perf_probe_api(perf_probe_cgroup);
    > +}
    > diff --git a/tools/perf/util/perf_api_probe.h b/tools/perf/util/perf_api_probe.h
    > index f12ca55f509a..b104168efb15 100644
    > --- a/tools/perf/util/perf_api_probe.h
    > +++ b/tools/perf/util/perf_api_probe.h
    > @@ -12,5 +12,6 @@ bool perf_can_record_switch_events(void);
    > bool perf_can_record_text_poke_events(void);
    > bool perf_can_sample_identifier(void);
    > bool perf_can_record_build_id(void);
    > +bool perf_can_record_cgroup(void);
    >
    > #endif // __PERF_API_PROBE_H
    > --
    > 2.32.0.rc0.204.g9fa02ecfa5-goog
    >

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