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add test for round robin threads #125

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add test for round robin threads #125

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6830a7f
scheduler: show Tick(id) for periodic_thread
lsf37 Jul 24, 2024
26ab769
scheduler: test round robin threads
lsf37 Jul 24, 2024
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71 changes: 70 additions & 1 deletion apps/sel4test-tests/src/tests/scheduler.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1038,7 +1038,7 @@ periodic_thread(int id, volatile unsigned long *counters)
while (1) {
counters[id]++;
test_leq(counters[id], (unsigned long) 10000);
printf("Tick\n");
printf("Tick (%d)\n", id);
seL4_Yield();
}
}
Expand Down Expand Up @@ -1695,3 +1695,72 @@ static int test_changing_affinity(struct env *env)
}
DEFINE_TEST(SCHED0022, "test changing a helper threads core", test_changing_affinity,
(config_set(CONFIG_KERNEL_MCS) &&(CONFIG_MAX_NUM_NODES > 1)));


/* busy wait for a number of iterations */
static void delay_loop(unsigned iterations) {
for (int i = 0; i < iterations; i++) {
__asm__ __volatile__ ("");
}
}

#define SCHED0023_NUM_ROUNDS 5

/* used in test_round_robin below */
static void round_robin_thread(int id, volatile unsigned long *counters)
{
delay_loop(id * 10000);

/* assumes counters are initialised already */
while (counters[id] < SCHED0023_NUM_ROUNDS) {
counters[id]++;
/* thread "id" should run after thread "id-1", so we should be at the same
count after incrementing if we are scheduled round robin. */
if (0 < id) {
test_eq(counters[id], counters[id - 1]);
}
printf("Tick (%d)\n", id);
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Maybe add a explicit note here that the blocking printing is not interfering with the test.

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I’m not sure it isn’t actually, I’m still experimenting. A good 30% of the configs where this test is enabled are still failing. But of course not when I’m trying to run it manually..

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I think it will interfere with the test, as it messes up all timing and hence scheduling.

/* busy wait so we can be preempted at least once before we increment
the counter again */
delay_loop(5000000);
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@axel-h axel-h Jul 25, 2024 •
edited
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Maybe add a note here why this magic value seem quite safe based on the assumption about time slice and core frequency/IPS.

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It looks like it isn’t safe yet on all machines, esp when printing is off. I might have to actually try to compute a value here instead. Just wanted to avoid making any syscalls in these threads that could affect scheduling.

}

test_eq(counters[id], (unsigned long) SCHED0023_NUM_ROUNDS);
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Maybe add a note there why this would ever fail. Is there any other cause besides memory corruption?

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Just making sure every thread is only writing to its own counter.

}

/* Test that round robin threads are indeed round robin. */
static int test_round_robin(struct env *env)
{
const int num_threads = 5;
helper_thread_t helpers[num_threads];
volatile unsigned long counters[num_threads];

for (int i = 0; i < num_threads; i++) {
counters[i] = 0;
create_helper_thread(env, &helpers[i]);
/* keep at lower priority first, we will drop our own priority when they are all started */
set_helper_priority(env, &helpers[i], env->priority - 1);
/* budget == priority makes them round robin */
set_helper_sched_params(env, &helpers[i], 1 * US_IN_MS, 1 * US_IN_MS, 0);
}

/* start in reverse order, because most recently started is first in scheduling
queue and we want id 0 to run first */
for (int i = num_threads - 1; i >= 0; i--) {
start_helper(env, &helpers[i],
(helper_fn_t) round_robin_thread, i, (seL4_Word) counters, 0, 0);
}

int error = seL4_TCB_SetPriority(env->tcb, env->tcb, env->priority - 2);
test_error_eq(error, seL4_NoError);

/* We will only get to run again when the round robin threads have all finished,
because they are higher priority */
for (int i = 0; i < num_threads; i++) {
test_eq(counters[i], (unsigned long) SCHED0023_NUM_ROUNDS);
}

return sel4test_get_result();
}
DEFINE_TEST(SCHED0023, "test round robin threads", test_round_robin,
(config_set(CONFIG_KERNEL_MCS)));
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