Re: [RFC v1 05/16] perf kwork: Overwrite original atom in the list when a new atom is pushed.

[Ian Rogers]

On Sat, Aug 12, 2023 at 1:52 AM Yang Jihong <yangjihong1@xxxxxxxxxx> wrote:
>
> work_push_atom() supports nesting. Currently, all supported kworks are not
> nested. A `overwrite` parameter is added to overwrite the original atom in
> the list.
>
> Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
> ---
>  tools/perf/builtin-kwork.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
>
> diff --git a/tools/perf/builtin-kwork.c b/tools/perf/builtin-kwork.c
> index 42ea59a957ae..f620911a26a2 100644
> --- a/tools/perf/builtin-kwork.c
> +++ b/tools/perf/builtin-kwork.c
> @@ -392,9 +392,10 @@ static int work_push_atom(struct perf_kwork *kwork,
>                           struct evsel *evsel,
>                           struct perf_sample *sample,
>                           struct machine *machine,
> -                         struct kwork_work **ret_work)
> +                         struct kwork_work **ret_work,
> +                         bool overwrite)

kerneldoc would be useful. Pushing something seems self-evident but
what does overwrite mean without reading the code?

>  {
> -       struct kwork_atom *atom, *dst_atom;
> +       struct kwork_atom *atom, *dst_atom, *last_atom;
>         struct kwork_work *work, key;
>
>         BUG_ON(class->work_init == NULL);
> @@ -427,6 +428,17 @@ static int work_push_atom(struct perf_kwork *kwork,
>         if (ret_work != NULL)
>                 *ret_work = work;
>
> +       if (overwrite) {
> +               last_atom = list_last_entry_or_null(&work->atom_list[src_type],
> +                                                   struct kwork_atom, list);
> +               if (last_atom) {
> +                       atom_del(last_atom);
> +
> +                       kwork->nr_skipped_events[src_type]++;
> +                       kwork->nr_skipped_events[KWORK_TRACE_MAX]++;
> +               }
> +       }
> +
>         list_add_tail(&atom->list, &work->atom_list[src_type]);
>
>         return 0;
> @@ -502,7 +514,7 @@ static int report_entry_event(struct perf_kwork *kwork,
>  {
>         return work_push_atom(kwork, class, KWORK_TRACE_ENTRY,
>                               KWORK_TRACE_MAX, evsel, sample,
> -                             machine, NULL);
> +                             machine, NULL, true);

nit: for constant arguments it can be useful to add parameter names
which can enable checks like clang-tidy's bugprone argument:
https://clang.llvm.org/extra/clang-tidy/checks/bugprone/argument-comment.html
This would make this:
        return work_push_atom(kwork, class, KWORK_TRACE_ENTRY,
                              KWORK_TRACE_MAX, evsel, sample,
                              machine, /*ret_work=*/NULL, /*overwite=*/true);

Thanks,
Ian

>  }
>
>  static int report_exit_event(struct perf_kwork *kwork,
> @@ -557,7 +569,7 @@ static int latency_raise_event(struct perf_kwork *kwork,
>  {
>         return work_push_atom(kwork, class, KWORK_TRACE_RAISE,
>                               KWORK_TRACE_MAX, evsel, sample,
> -                             machine, NULL);
> +                             machine, NULL, true);
>  }
>
>  static int latency_entry_event(struct perf_kwork *kwork,
> @@ -716,7 +728,7 @@ static int timehist_raise_event(struct perf_kwork *kwork,
>  {
>         return work_push_atom(kwork, class, KWORK_TRACE_RAISE,
>                               KWORK_TRACE_MAX, evsel, sample,
> -                             machine, NULL);
> +                             machine, NULL, true);
>  }
>
>  static int timehist_entry_event(struct perf_kwork *kwork,
> @@ -730,7 +742,7 @@ static int timehist_entry_event(struct perf_kwork *kwork,
>
>         ret = work_push_atom(kwork, class, KWORK_TRACE_ENTRY,
>                              KWORK_TRACE_RAISE, evsel, sample,
> -                            machine, &work);
> +                            machine, &work, true);
>         if (ret)
>                 return ret;
>
> --
> 2.30.GIT
>