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tests/kernel/sched/schedule_api: Relax preemption order constraints

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This test was testing for an undocumented and somewhat hyperspecific
behavior: when a process reaches a reschedule point and yields to a
higher priority thread, and there is another equal priority thread
active, which thread gets to run when the higher priority thread
finishes its work?  The original scheduler (because it leaves the
older thread in place in the list) implements the preemption like an
interrupt and returns to the original thread, despite the fact that
this then resets is time slice quantum unfairly.  In SMP mode, where
the current threads cannot live in the active list, the thread gets
added back to the end of the queue and the other thread runs.  In
effect, in UP mode "yield" and "reschedule" mean very slightly
different things where in SMP they act the same.

We don't document either behavior, as it happens.  Relax the test
constraints by adding a single deliberate k_yield() to unify behavior.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
This commit is contained in:
Andy Ross 2019-08-21 20:49:32 -07:00 • committed by Anas Nashif
commit 49398cfbf6
1 changed files with 13 additions and 7 deletions
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20
tests/kernel/sched/schedule_api/src/test_sched_timeslice_and_lock.c
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@ -356,11 +356,15 @@ void test_unlock_preemptible(void)
k_busy_wait(100000);
k_sched_unlock();
/* checkpoint: higher threads get executed */
/* ensure threads of equal priority can run */
k_yield();
/* checkpoint: higher and equal threads get executed */
zassert_true(tdata[0].executed == 1, NULL);
for (int i = 1; i < THREADS_NUM; i++) {
zassert_true(tdata[i].executed == 0, NULL);
}
zassert_true(tdata[1].executed == 1, NULL);
zassert_true(tdata[2].executed == 0, NULL);
/* restore environment */
teardown_threads();
}
@ -404,11 +408,13 @@ void test_unlock_nested_sched_lock(void)
/* unlock another; this let the higher thread to run */
k_sched_unlock();
/* Ensure threads of equal priority run */
k_yield();
/* checkpoint: higher threads NOT get executed */
zassert_true(tdata[0].executed == 1, NULL);
for (int i = 1; i < THREADS_NUM; i++) {
zassert_true(tdata[i].executed == 0, NULL);
}
zassert_true(tdata[1].executed == 1, NULL);
zassert_true(tdata[2].executed == 0, NULL);
/* restore environment */
teardown_threads();