Re: [PATCH] perf util: Use target->per_thread and target->system_wide flags

[Mathieu Poirier]

On 22 January 2018 at 15:15, Jin Yao <yao.jin@xxxxxxxxxxxxxxx> wrote:
> Mathieu Poirier reports issue in commit ("73c0ca1eee3d perf thread_map:
> Enumerate all threads from /proc") that it has negative impact on
> 'perf record --per-thread'. It has the effect of creating a kernel event
> for each thread in the system for 'perf record --per-thread'.
>
> Mathieu Poirier's patch ("perf util: Do not reuse target->per_thread flag")
> can fix this issue by creating a new target->all_threads flag.
>
> This patch is based on Mathieu Poirier's patch but it doesn't use a new
> target->all_threads flag. This patch just uses 'target->per_thread &&
> target->system_wide' as a condition to check for all threads case.
>
> Signed-off-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
> ---
>  tools/perf/util/evlist.c     | 2 +-
>  tools/perf/util/thread_map.c | 4 ++--
>  tools/perf/util/thread_map.h | 2 +-
>  3 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 120efd8..9dff74a 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -1106,7 +1106,7 @@ int perf_evlist__create_maps(struct perf_evlist *evlist, struct target *target)
>         struct thread_map *threads;
>
>         threads = thread_map__new_str(target->pid, target->tid, target->uid,
> -                                     target->per_thread);
> +                                     target->per_thread && target->system_wide);

At first glance I thought your solution would do the trick but perf
record does use target->system_wide when the '-a' switch is used.
Moreover specifying the '-a' switch doesn't prevent the '--per-thread'
option from being used as well, making both target->perf_thread and
target_system_wide equal to true (and that is not good).

Although not a fan of adding more to struct target, the advantage of
having target->all_threads is that we are guaranteed that it isn't
used anywhere else.

Let me know what you think,
Mathieu

>
>         if (!threads)
>                 return -1;
> diff --git a/tools/perf/util/thread_map.c b/tools/perf/util/thread_map.c
> index 3e1038f..729dad8 100644
> --- a/tools/perf/util/thread_map.c
> +++ b/tools/perf/util/thread_map.c
> @@ -323,7 +323,7 @@ struct thread_map *thread_map__new_by_tid_str(const char *tid_str)
>  }
>
>  struct thread_map *thread_map__new_str(const char *pid, const char *tid,
> -                                      uid_t uid, bool per_thread)
> +                                      uid_t uid, bool all_threads)
>  {
>         if (pid)
>                 return thread_map__new_by_pid_str(pid);
> @@ -331,7 +331,7 @@ struct thread_map *thread_map__new_str(const char *pid, const char *tid,
>         if (!tid && uid != UINT_MAX)
>                 return thread_map__new_by_uid(uid);
>
> -       if (per_thread)
> +       if (all_threads)
>                 return thread_map__new_all_cpus();
>
>         return thread_map__new_by_tid_str(tid);
> diff --git a/tools/perf/util/thread_map.h b/tools/perf/util/thread_map.h
> index 0a806b9..5ec91cf 100644
> --- a/tools/perf/util/thread_map.h
> +++ b/tools/perf/util/thread_map.h
> @@ -31,7 +31,7 @@ struct thread_map *thread_map__get(struct thread_map *map);
>  void thread_map__put(struct thread_map *map);
>
>  struct thread_map *thread_map__new_str(const char *pid,
> -               const char *tid, uid_t uid, bool per_thread);
> +               const char *tid, uid_t uid, bool all_threads);
>
>  struct thread_map *thread_map__new_by_tid_str(const char *tid_str);
>
> --
> 2.7.4
>