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

[Namhyung Kim <namhyung@kernel.org>]

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 <namhyung@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