[LTP] [PATCH 3/6] sched_football: Re-add the crazy fans to interrupt everyone

[John Stultz]

An idea that I had included long ago in this test case, but was
later dropped was the "crazy fans", which added extra disruption
to the scheduling behavior.

In my recent work, I've found that including them uncovers some
unexpected behavior with current Linux kernels.

So re-add the high priroity tasks that wake up and run to disrupt
the scheduling of defense threads. We run 2*NR_CPU "fan" threads
and they spin for awhile, to force migrations.

Cc: kernel-team@android.com
Cc: Darren Hart <darren@os.amperecomputing.com>
Signed-off-by: John Stultz <jstultz@google.com>
---
 .../func/sched_football/sched_football.c      | 63 ++++++++++++++++---
 1 file changed, 55 insertions(+), 8 deletions(-)

diff --git a/testcases/realtime/func/sched_football/sched_football.c b/testcases/realtime/func/sched_football/sched_football.c
index 359c96703..ed3c5cadf 100644
--- a/testcases/realtime/func/sched_football/sched_football.c
+++ b/testcases/realtime/func/sched_football/sched_football.c
@@ -22,19 +22,23 @@
  * DESCRIPTION
  *      This is a scheduler test that uses a football analogy.
  *      The premise is that we want to make sure that lower priority threads
- *      (defensive team). The offense is trying to increment the balls position,
- *      while the defense is trying to block that from happening.
+ *      don't run while we have runnable higher priority threads.
+ *      The offense is trying to increment the balls position, while the
+ *      defense is trying to block that from happening.
  *      And the ref (highest priority thread) will blow the wistle if the
  *      ball moves. Finally, we have crazy fans (higer prority) that try to
  *      distract the defense by occasionally running onto the field.
  *
  *      Steps:
- *       - Create a fixed number of offense threads (lower priority)
+ *       - Create NR_CPU offense threads (lower priority)
+ *       - Create NR_CPU defense threads (mid priority)
+ *       - Create 2*NR_CPU fan threads (high priority)
  *       - Create a referee thread (highest priority)
- *       - Once everyone is on the field, the offense thread increments the
- *         value of 'the_ball'. The defense thread tries to block
- *         the ball by never letting the offense players get the CPU (it just
- *         spins).
+ *       - Once everyone is on the field, the offense thread spins incrementing
+ *         the value of 'the_ball'. The defense thread tries to block the ball
+ *         by never letting the offense players get the CPU (it just spins).
+ *         The crazy fans sleep a bit, then jump the rail and run across the
+ *         field, disrupting the players on the field.
  *       - The refree threads wakes up regularly to check if the game is over :)
  *       - In the end, if the value of 'the_ball' is >0, the test is considered
  *         to have failed.
@@ -52,7 +56,7 @@
  *		bugfixes and cleanups. -- Josh Triplett
  *     2009-06-23 Simplified atomic startup mechanism, avoiding thundering herd
  *		scheduling at the beginning of the game. -- Darren Hart
- *
+ *     2024-04-23 Re-add crazy fans! Along with minor cleanups -- John Stultz
  *****************************************************************************/
 
 #include <stdio.h>
@@ -107,6 +111,38 @@ int parse_args(int c, char *v)
 	return handled;
 }
 
+#define NSEC_PER_SEC 1000000000ULL
+unsigned long long ts_delta(struct timespec *start, struct timespec *stop)
+{
+	unsigned long long a, b;
+
+	a = start->tv_sec * NSEC_PER_SEC + start->tv_nsec;
+	b = stop->tv_sec * NSEC_PER_SEC + stop->tv_nsec;
+	return b - a;
+}
+
+#define SPIN_TIME_NS 200000000
+#define SLEEP_TIME_NS 50000000
+/* These are fans running across the field. They're trying to interrupt/distract everyone */
+void *thread_fan(void *arg)
+{
+	atomic_inc(&players_ready);
+	/*occasionally wake up and run across the field */
+	while (1) {
+		int i;
+		struct timespec start, stop;
+
+		start.tv_sec = 0;
+		start.tv_nsec = SLEEP_TIME_NS;
+		clock_nanosleep(CLOCK_MONOTONIC, 0, &start, NULL);
+		clock_gettime(CLOCK_MONOTONIC, &start);
+		clock_gettime(CLOCK_MONOTONIC, &stop);
+		while (ts_delta(&start, &stop) < SPIN_TIME_NS)
+			clock_gettime(CLOCK_MONOTONIC, &stop);
+	}
+	return NULL;
+}
+
 /* This is the defensive team. They're trying to block the offense */
 void *thread_defense(void *arg)
 {
@@ -199,6 +235,17 @@ int main(int argc, char *argv[])
 	while (atomic_get(&players_ready) < players_per_team * 2)
 		usleep(100);
 
+	/* Start the crazy fans*/
+	priority = 50;
+	printf("Starting %d fan threads at priority %d\n",
+	       players_per_team, priority);
+	for (i = 0; i < players_per_team*2; i++)
+		create_fifo_thread(thread_fan, NULL, priority);
+
+	/* Wait for the crazy fan threads to start */
+	while (atomic_get(&players_ready) < players_per_team * 4)
+		usleep(100);
+
 	/* Ok, everyone is on the field, bring out the ref */
 	printf("Starting referee thread\n");
 	result = referee(game_length);
-- 
2.44.0.769.g3c40516874-goog