[PATCH] perf: sched: Show start of latency as well

[Joel Fernandes (Google)]

perf sched latency is really useful at showing worst-case latencies that task
encountered since wakeup. However it shows only the end of the latency. Often
times the start of a latency is interesting as it can show what else was going
on at the time to cause the latency. I certainly myself spending a lot of time
backtracking to the start of the latency in "perf sched script" which wastes a
lot of time.

This patch therefore adds a new column "Max delay start". Considering this,
also rename "Maximum delay at" to "Max delay end" as its easier to understand.

Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>


---
A sample output can be seen after applying patch:
https://hastebin.com/raw/ivinimaler

 tools/perf/builtin-sched.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 459e4229945e..2791da1fe5f7 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -130,7 +130,8 @@ struct work_atoms {
 	struct thread		*thread;
 	struct rb_node		node;
 	u64			max_lat;
-	u64			max_lat_at;
+	u64			max_lat_start;
+	u64			max_lat_end;
 	u64			total_lat;
 	u64			nb_atoms;
 	u64			total_runtime;
@@ -1096,7 +1097,8 @@ add_sched_in_event(struct work_atoms *atoms, u64 timestamp)
 	atoms->total_lat += delta;
 	if (delta > atoms->max_lat) {
 		atoms->max_lat = delta;
-		atoms->max_lat_at = timestamp;
+		atoms->max_lat_start = atom->wake_up_time;
+		atoms->max_lat_end = timestamp;
 	}
 	atoms->nb_atoms++;
 }
@@ -1322,7 +1324,7 @@ static void output_lat_thread(struct perf_sched *sched, struct work_atoms *work_
 	int i;
 	int ret;
 	u64 avg;
-	char max_lat_at[32];
+	char max_lat_start[32], max_lat_end[32];
 
 	if (!work_list->nb_atoms)
 		return;
@@ -1344,13 +1346,14 @@ static void output_lat_thread(struct perf_sched *sched, struct work_atoms *work_
 		printf(" ");
 
 	avg = work_list->total_lat / work_list->nb_atoms;
-	timestamp__scnprintf_usec(work_list->max_lat_at, max_lat_at, sizeof(max_lat_at));
+	timestamp__scnprintf_usec(work_list->max_lat_start, max_lat_start, sizeof(max_lat_start));
+	timestamp__scnprintf_usec(work_list->max_lat_end, max_lat_end, sizeof(max_lat_end));
 
-	printf("|%11.3f ms |%9" PRIu64 " | avg:%9.3f ms | max:%9.3f ms | max at: %13s s\n",
+	printf("|%11.3f ms |%9" PRIu64 " | avg:%8.3f ms | max:%8.3f ms | max start: %12s s | max end: %12s s\n",
 	      (double)work_list->total_runtime / NSEC_PER_MSEC,
 		 work_list->nb_atoms, (double)avg / NSEC_PER_MSEC,
 		 (double)work_list->max_lat / NSEC_PER_MSEC,
-		 max_lat_at);
+		 max_lat_start, max_lat_end);
 }
 
 static int pid_cmp(struct work_atoms *l, struct work_atoms *r)
@@ -3118,7 +3121,8 @@ static void __merge_work_atoms(struct rb_root_cached *root, struct work_atoms *d
 			list_splice(&data->work_list, &this->work_list);
 			if (this->max_lat < data->max_lat) {
 				this->max_lat = data->max_lat;
-				this->max_lat_at = data->max_lat_at;
+				this->max_lat_start = data->max_lat_start;
+				this->max_lat_end = data->max_lat_end;
 			}
 			zfree(&data);
 			return;
@@ -3157,9 +3161,9 @@ static int perf_sched__lat(struct perf_sched *sched)
 	perf_sched__merge_lat(sched);
 	perf_sched__sort_lat(sched);
 
-	printf("\n -----------------------------------------------------------------------------------------------------------------\n");
-	printf("  Task                  |   Runtime ms  | Switches | Average delay ms | Maximum delay ms | Maximum delay at       |\n");
-	printf(" -----------------------------------------------------------------------------------------------------------------\n");
+	printf("\n -------------------------------------------------------------------------------------------------------------------------------------------\n");
+	printf("  Task                  |   Runtime ms  | Switches | Avg delay ms    | Max delay ms    | Max delay start           | Max delay end          |\n");
+	printf(" -------------------------------------------------------------------------------------------------------------------------------------------\n");
 
 	next = rb_first_cached(&sched->sorted_atom_root);
 
-- 
2.28.0.709.gb0816b6eb0-goog