Re: [PATCH V1 13/23] perf evlist: Add evlist__add_system_wide_dummy()

[Ian Rogers <irogers@google.com>]

On Thu, May 5, 2022 at 9:57 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>
> Add evlist__add_system_wide_dummy() to enable creating a system-wide dummy
> event that sets up the system-wide maps before map propagation.

Perhaps this should be:
evlist__add_dummy_on_all_online_cpus()
my thoughts being that a system wide dummy sounds like the dummy CPU
map, ie {-1} whilst what happens here is opening on all online CPUs
{0-35} on a 36 hyperthread system. Note also that the libperf
cpu_map__read_all_cpu_map code doesn't discover sysfs' mount properly,
as done in:
tools/lib/api/fs/fs.h
Some tech debt.

> For convenience, add evlist__add_aux_dummy() so that the logic can be used
> whether or not the event needs to be system-wide.
>
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> ---
>  tools/perf/util/evlist.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  tools/perf/util/evlist.h |  5 +++++
>  2 files changed, 45 insertions(+)
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 78c47cbafbc2..58ea562ddbd2 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -264,6 +264,46 @@ int evlist__add_dummy(struct evlist *evlist)
>         return 0;
>  }
>
> +static void evlist__add_system_wide(struct evlist *evlist, struct evsel *evsel)

This would be:
evlist__add_on_all_online_cpus(..)

> +{
> +       evsel->core.system_wide = true;
> +
> +       /* All CPUs */
> +       perf_cpu_map__put(evsel->core.own_cpus);
> +       evsel->core.own_cpus = perf_cpu_map__new(NULL);
> +       perf_cpu_map__put(evsel->core.cpus);
> +       evsel->core.cpus = perf_cpu_map__get(evsel->core.own_cpus);
> +
> +       /* No threads */
> +       perf_thread_map__put(evsel->core.threads);
> +       evsel->core.threads = perf_thread_map__new_dummy();
> +
> +       evlist__add(evlist, evsel);
> +}
> +
> +struct evsel *evlist__add_aux_dummy(struct evlist *evlist, bool system_wide)
> +{
> +       struct evsel *evsel = evlist__dummy_event(evlist);
> +
> +       if (!evsel)
> +               return NULL;
> +
> +       evsel->core.attr.exclude_kernel = 1;
> +       evsel->core.attr.exclude_guest = 1;
> +       evsel->core.attr.exclude_hv = 1;
> +       evsel->core.attr.freq = 0;
> +       evsel->core.attr.sample_period = 1;
> +       evsel->no_aux_samples = true;
> +       evsel->name = strdup("dummy:u");
> +
> +       if (system_wide)
> +               evlist__add_system_wide(evlist, evsel);
> +       else
> +               evlist__add(evlist, evsel);
> +
> +       return evsel;
> +}
> +
>  static int evlist__add_attrs(struct evlist *evlist, struct perf_event_attr *attrs, size_t nr_attrs)
>  {
>         struct evsel *evsel, *n;
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 4062f5aebfc1..dd1af114e033 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -114,6 +114,11 @@ int arch_evlist__add_default_attrs(struct evlist *evlist);
>  struct evsel *arch_evlist__leader(struct list_head *list);
>
>  int evlist__add_dummy(struct evlist *evlist);
> +struct evsel *evlist__add_aux_dummy(struct evlist *evlist, bool system_wide);
> +static inline struct evsel *evlist__add_system_wide_dummy(struct evlist *evlist)
> +{
> +       return evlist__add_aux_dummy(evlist, true);
> +}
>
>  int evlist__add_sb_event(struct evlist *evlist, struct perf_event_attr *attr,
>                          evsel__sb_cb_t cb, void *data);
> --
> 2.25.1
>