Re: [PATCH v1 2/6] perf trace: Ignore thread hashing in summary

[Namhyung Kim <namhyung@kernel.org>]

On Tue, Feb 13, 2024 at 10:37 PM Ian Rogers <irogers@google.com> wrote:
>
> Commit 91e467bc568f ("perf machine: Use hashtable for machine
> threads") made the iteration of thread tids unordered. The perf trace
> --summary output sorts and prints each hash bucket, rather than all
> threads globally. Change this behavior by turn all threads into a
> list, sort the list by number of trace events then by tids, finally
> print the list. This also allows the rbtree in threads to be not
> accessed outside of machine.
>
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>  tools/perf/builtin-trace.c  | 41 +++++++++++++++++++++----------------
>  tools/perf/util/rb_resort.h |  5 -----
>  2 files changed, 23 insertions(+), 23 deletions(-)
>
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index 109b8e64fe69..90eaff8c0f6e 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -74,6 +74,7 @@
>  #include <linux/err.h>
>  #include <linux/filter.h>
>  #include <linux/kernel.h>
> +#include <linux/list_sort.h>
>  #include <linux/random.h>
>  #include <linux/stringify.h>
>  #include <linux/time64.h>
> @@ -4312,34 +4313,38 @@ static unsigned long thread__nr_events(struct thread_trace *ttrace)
>         return ttrace ? ttrace->nr_events : 0;
>  }
>
> -DEFINE_RESORT_RB(threads,
> -               (thread__nr_events(thread__priv(a->thread)) <
> -                thread__nr_events(thread__priv(b->thread))),
> -       struct thread *thread;
> -)
> +static int trace_nr_events_cmp(void *priv __maybe_unused,
> +                              const struct list_head *la,
> +                              const struct list_head *lb)
>  {
> -       entry->thread = rb_entry(nd, struct thread_rb_node, rb_node)->thread;
> +       struct thread_list *a = list_entry(la, struct thread_list, list);
> +       struct thread_list *b = list_entry(lb, struct thread_list, list);
> +       unsigned long a_nr_events = thread__nr_events(thread__priv(a->thread));
> +       unsigned long b_nr_events = thread__nr_events(thread__priv(b->thread));
> +
> +       if (a_nr_events != b_nr_events)
> +               return a_nr_events < b_nr_events ? -1 : 1;
> +
> +       /* Identical number of threads, place smaller tids first. */
> +       return thread__tid(a->thread) < thread__tid(b->thread)
> +               ? -1
> +               : (thread__tid(a->thread) > thread__tid(b->thread) ? 1 : 0);

I'm not sure if it can have a case where two different threads in the
hash table can have the same tid.  If not, it can simplify the last case.


>  }
>
>  static size_t trace__fprintf_thread_summary(struct trace *trace, FILE *fp)
>  {
>         size_t printed = trace__fprintf_threads_header(fp);
> -       struct rb_node *nd;
> -       int i;
> -
> -       for (i = 0; i < THREADS__TABLE_SIZE; i++) {
> -               DECLARE_RESORT_RB_MACHINE_THREADS(threads, trace->host, i);
> +       LIST_HEAD(threads);
>
> -               if (threads == NULL) {
> -                       fprintf(fp, "%s", "Error sorting output by nr_events!\n");
> -                       return 0;
> -               }
> +       if (machine__thread_list(trace->host, &threads) == 0) {
> +               struct thread_list *pos;
>
> -               resort_rb__for_each_entry(nd, threads)
> -                       printed += trace__fprintf_thread(fp, threads_entry->thread, trace);
> +               list_sort(NULL, &threads, trace_nr_events_cmp);

Same concern, it'd be nice if we can use an array instead.

Thanks,
Namhyung


>
> -               resort_rb__delete(threads);
> +               list_for_each_entry(pos, &threads, list)
> +                       printed += trace__fprintf_thread(fp, pos->thread, trace);
>         }
> +       thread_list__delete(&threads);
>         return printed;
>  }
>
> diff --git a/tools/perf/util/rb_resort.h b/tools/perf/util/rb_resort.h
> index 376e86cb4c3c..d927a0d25052 100644
> --- a/tools/perf/util/rb_resort.h
> +++ b/tools/perf/util/rb_resort.h
> @@ -143,9 +143,4 @@ struct __name##_sorted *__name = __name##_sorted__new
>         DECLARE_RESORT_RB(__name)(&__ilist->rblist.entries.rb_root,             \
>                                   __ilist->rblist.nr_entries)
>
> -/* For 'struct machine->threads' */
> -#define DECLARE_RESORT_RB_MACHINE_THREADS(__name, __machine, hash_bucket)    \
> - DECLARE_RESORT_RB(__name)(&__machine->threads[hash_bucket].entries.rb_root, \
> -                          __machine->threads[hash_bucket].nr)
> -
>  #endif /* _PERF_RESORT_RB_H_ */
> --
> 2.43.0.687.g38aa6559b0-goog
>