[LTP] LTP Release preparations

[Li Wang]

Hi Cyril, Andrea,

On Wed, Sep 3, 2025 at 9:20 PM Cyril Hrubis <chrubis@suse.cz> wrote:

> Hi!
> > > After an analysis we are now sure that it's not a product bug but a
> test
> > > issue. There might be a need to fallback the patch if we can't fix the
> > > test before release. @Li WDYT?

>
> > Try this:
> >
> > diff --git a/testcases/realtime/func/sched_football/sched_football.c
> b/testcases/realtime/func/sched_football/sched_football.c
> > index 0617bdb87..0d64210b0 100644
> > --- a/testcases/realtime/func/sched_football/sched_football.c
> > +++ b/testcases/realtime/func/sched_football/sched_football.c
> > @@ -115,8 +115,8 @@ void referee(int game_length)
> >         now = start;
> >
> >         /* Start the game! */
> > -       tst_atomic_store(0, &the_ball);
> >         pthread_barrier_wait(&start_barrier);
> > +       tst_atomic_store(0, &the_ball);
> >         atrace_marker_write("sched_football", "Game_started!");
> >
> >
> > We have to be sure that the defense has started before we clear the
> > ball. Previously we had the loop that waited for the players to be ready
> > before we called referee() function so all the players were ready when
> > we cleared it.
>
> Uff and we have to get the final ball position before we stop the
> threads as well, otherwise there is always chance, that we may end up
> moving the ball right after the high priority defence threads has been
> stopped:
>

This makes sense! However, from my extensive testing, I still see
occasional fails on KVM/Debug platforms.

I suspect the existing barriers ensure all threads are created before
the game starts, but small scheduler skews can still allow the attacking
thread to run for a few cycles before the defending thread migrates,
especially on debug/RT kernels.

So, based on this improve, we might need additional spin for all player
threads (offense, defense, fans) wait at the barrier and then spin until
the referee kicks off the ball.

--- a/testcases/realtime/func/sched_football/sched_football.c
+++ b/testcases/realtime/func/sched_football/sched_football.c
@@ -44,6 +44,7 @@
 static tst_atomic_t the_ball;
 static int players_per_team = 0;
 static int game_length = DEF_GAME_LENGTH;
+static tst_atomic_t kickoff_flag;
 static tst_atomic_t game_over;

 static char *str_game_length;
@@ -55,6 +56,9 @@ void *thread_fan(void *arg LTP_ATTRIBUTE_UNUSED)
 {
        prctl(PR_SET_NAME, "crazy_fan", 0, 0, 0);
        pthread_barrier_wait(&start_barrier);
+       while (!tst_atomic_load(&kickoff_flag))
+               ;
+
        /*occasionally wake up and run across the field */
        while (!tst_atomic_load(&game_over)) {
                struct timespec start, stop;
@@ -80,6 +84,9 @@ void *thread_defense(void *arg LTP_ATTRIBUTE_UNUSED)
 {
        prctl(PR_SET_NAME, "defense", 0, 0, 0);
        pthread_barrier_wait(&start_barrier);
+       while (!tst_atomic_load(&kickoff_flag))
+               ;
+
        /*keep the ball from being moved */
        while (!tst_atomic_load(&game_over)) {
        }
@@ -92,6 +99,9 @@ void *thread_offense(void *arg LTP_ATTRIBUTE_UNUSED)
 {
        prctl(PR_SET_NAME, "offense", 0, 0, 0);
        pthread_barrier_wait(&start_barrier);
+       while (!tst_atomic_load(&kickoff_flag))
+               ;
+
        while (!tst_atomic_load(&game_over)) {
                tst_atomic_add_return(1, &the_ball); /* move the ball ahead
one yard */
        }
@@ -115,9 +125,10 @@ void referee(int game_length)
        now = start;

        /* Start the game! */
-       tst_atomic_store(0, &the_ball);
-       pthread_barrier_wait(&start_barrier);
        atrace_marker_write("sched_football", "Game_started!");
+       pthread_barrier_wait(&start_barrier);
+       tst_atomic_store(0, &the_ball);
+       tst_atomic_store(1, &kickoff_flag);

        /* Watch the game */
        while ((now.tv_sec - start.tv_sec) < game_length) {
@@ -125,14 +136,14 @@ void referee(int game_length)
                gettimeofday(&now, NULL);
        }

-       /* Stop the game! */
-       tst_atomic_store(1, &game_over);
-       atrace_marker_write("sched_football", "Game_Over!");
-
        /* Blow the whistle */
        final_ball = tst_atomic_load(&the_ball);
        tst_res(TINFO, "Final ball position: %d", final_ball);

+       /* Stop the game! */
+       tst_atomic_store(1, &game_over);
+       atrace_marker_write("sched_football", "Game_Over!");
+
        TST_EXP_EXPR(final_ball == 0);
 }

@@ -154,6 +165,7 @@ static void do_test(void)
        /* We're the ref, so set our priority right */
        param.sched_priority = sched_get_priority_min(SCHED_FIFO) + 80;
        sched_setscheduler(0, SCHED_FIFO, &param);
+       tst_atomic_store(0, &kickoff_flag);

        /*
         * Start the offense


>
> diff --git a/testcases/realtime/func/sched_football/sched_football.c
> b/testcases/realtime/func/sched_football/sched_football.c
> index 0617bdb87..54317bed9 100644
> --- a/testcases/realtime/func/sched_football/sched_football.c
> +++ b/testcases/realtime/func/sched_football/sched_football.c
> @@ -115,8 +115,8 @@ void referee(int game_length)
>         now = start;
>
>         /* Start the game! */
> -       tst_atomic_store(0, &the_ball);
>         pthread_barrier_wait(&start_barrier);
> +       tst_atomic_store(0, &the_ball);
>         atrace_marker_write("sched_football", "Game_started!");
>
>         /* Watch the game */
> @@ -125,14 +125,14 @@ void referee(int game_length)
>                 gettimeofday(&now, NULL);
>         }
>
> -       /* Stop the game! */
> -       tst_atomic_store(1, &game_over);
> -       atrace_marker_write("sched_football", "Game_Over!");
> -
>         /* Blow the whistle */
>         final_ball = tst_atomic_load(&the_ball);
>         tst_res(TINFO, "Final ball position: %d", final_ball);
>
> +       /* Stop the game! */
> +       tst_atomic_store(1, &game_over);
> +       atrace_marker_write("sched_football", "Game_Over!");
> +
>         TST_EXP_EXPR(final_ball == 0);
>  }
>
>
> --
> Cyril Hrubis
> chrubis@suse.cz
>
> --
> Mailing list info: https://lists.linux.it/listinfo/ltp
>
>

-- 
Regards,
Li Wang