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| author | Adrian Hunter <adrian.hunter@intel.com> | 2018-12-21 14:06:20 +0200 |
|---|---|---|
| committer | Arnaldo Carvalho de Melo <acme@redhat.com> | 2019-01-02 11:05:06 -0300 |
| commit | b25756df5b28cd7b6e91200fc5012e7c76e8ec69 (patch) | |
| tree | 0dac9718cbb0de36b66b45f9d1d7a8d2b01c32ad | |
| parent | 256d92bc93fd40411a02be5cdba74a7bf91e6e09 (diff) | |
perf session: Add comment for perf_session__register_idle_thread()
Add a comment to perf_session__register_idle_thread() to bring attention to
a pitfall with the idle task thread structure. The pitfall is that there
should really be a 'struct thread' for the idle task of each cpu, but there
is only one that can have pid == tid == 0.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20181221120620.9659-9-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
| -rw-r--r-- | tools/perf/util/session.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c index 78a067777144..5456c84c7dd1 100644 --- a/tools/perf/util/session.c +++ b/tools/perf/util/session.c @@ -1527,6 +1527,13 @@ struct thread *perf_session__findnew(struct perf_session *session, pid_t pid) return machine__findnew_thread(&session->machines.host, -1, pid); } +/* + * Threads are identified by pid and tid, and the idle task has pid == tid == 0. + * So here a single thread is created for that, but actually there is a separate + * idle task per cpu, so there should be one 'struct thread' per cpu, but there + * is only 1. That causes problems for some tools, requiring workarounds. For + * example get_idle_thread() in builtin-sched.c, or thread_stack__per_cpu(). + */ int perf_session__register_idle_thread(struct perf_session *session) { struct thread *thread; |