[PATCH v2 3/6] perf sched timehist: Save callchain when entering idle

[Namhyung Kim]

In order to investigate reason of idle, it needs to keep the callchains
when entering to idle.  This can be identified sched_switch event having
next_pid as 0.

Signed-off-by: Namhyung Kim <namhy...@kernel.org>
---
 tools/perf/builtin-sched.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 6f0687dd392d..4c5c58ce8958 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -200,6 +200,7 @@ struct perf_sched {
        /* options for timehist command */
        bool            summary;
        bool            summary_only;
+       bool            idle_hist;
        bool            show_callchain;
        unsigned int    max_stack;
        bool            show_cpu_visual;
@@ -2101,6 +2102,29 @@ static struct thread *get_idle_thread(int cpu)
        return idle_threads[cpu];
 }
 
+static void save_idle_callchain(struct thread *thread,
+                               struct perf_sample *sample)
+{
+       struct thread *idle;
+       struct idle_thread_runtime *itr;
+
+       if (!symbol_conf.use_callchain || sample->callchain == NULL)
+               return;
+
+       idle = get_idle_thread(sample->cpu);
+       if (idle == NULL) {
+               pr_err("Failed to get idle thread for cpu %d.\n", sample->cpu);
+               return;
+       }
+
+       itr = thread__priv(idle);
+       if (itr == NULL)
+               return;
+
+       itr->last_thread = thread;
+       callchain_cursor__copy(&itr->cursor, &callchain_cursor);
+}
+
 /*
  * handle runtime stats saved per thread
  */
@@ -2154,6 +2178,11 @@ static struct thread *timehist_get_thread(struct 
perf_sched *sched,
                }
 
                save_task_callchain(sched, sample, evsel, machine);
+               if (sched->idle_hist) {
+                       /* copy task callchain when entering to idle */
+                       if (perf_evsel__intval(evsel, sample, "next_pid") == 0)
+                               save_idle_callchain(thread, sample);
+               }
        }
 
        return thread;
-- 
2.10.1