sched: timeout: Do not miss slice timeouts
Time slices don't have a timeout struct associated and stored in
timeout_list. Time slice timeout is direct programmed in the system
clock and tracked in _current_cpu->slice_ticks.
There is one issue where the time slice timeout can be missed because
the system clock is re-programmed to a longer timeout. To this happens,
it is only necessary that the timeout_list is empty (any timeout set)
and a new timeout longer than remaining time slice is set. This is cause
because z_add_timeout does not check for the slice ticks.
The following example spots the issue:
K_THREAD_STACK_DEFINE(tstack, STACK_SIZE);
K_THREAD_STACK_ARRAY_DEFINE(tstacks, NUM_THREAD, STACK_SIZE);
K_SEM_DEFINE(sema, 0, NUM_THREAD);
static inline void spin_for_ms(int ms)
{
uint32_t t32 = k_uptime_get_32();
while (k_uptime_get_32() - t32 < ms) {
}
}
static void thread_time_slice(void *p1, void *p2, void *p3)
{
printk("thread[%d] - Before spin\n", (int)(uintptr_t)p1);
/* Spinning for longer than slice */
spin_for_ms(SLICE_SIZE + 20);
/* The following print should not happen before another
* same priority thread starts.
*/
printk("thread[%d] - After spinning\n", (int)(uintptr_t)p1);
k_sem_give(&sema);
}
void main(void)
{
k_tid_t tid[NUM_THREAD];
struct k_thread t[NUM_THREAD];
uint32_t slice_ticks = k_ms_to_ticks_ceil32(SLICE_SIZE);
int old_prio = k_thread_priority_get(k_current_get());
/* disable timeslice */
k_sched_time_slice_set(0, K_PRIO_PREEMPT(0));
for (int j = 0; j < 2; j++) {
k_sem_reset(&sema);
/* update priority for current thread */
k_thread_priority_set(k_current_get(), K_PRIO_PREEMPT(j));
/* synchronize to tick boundary */
k_usleep(1);
/* create delayed threads with equal preemptive priority */
for (int i = 0; i < NUM_THREAD; i++) {
tid[i] = k_thread_create(&t[i], tstacks[i], STACK_SIZE,
thread_time_slice, (void *)i, NULL,
NULL, K_PRIO_PREEMPT(j), 0,
K_NO_WAIT);
}
/* enable time slice (and reset the counter!) */
k_sched_time_slice_set(SLICE_SIZE, K_PRIO_PREEMPT(0));
/* Spins for while to spend this thread time but not longer */
/* than a slice. This is important */
spin_for_ms(100);
printk("before sleep\n");
/* relinquish CPU and wait for each thread to complete */
k_sleep(K_TICKS(slice_ticks * (NUM_THREAD + 1)));
for (int i = 0; i < NUM_THREAD; i++) {
k_sem_take(&sema, K_FOREVER);
}
/* test case teardown */
for (int i = 0; i < NUM_THREAD; i++) {
k_thread_abort(tid[i]);
}
/* disable time slice */
k_sched_time_slice_set(0, K_PRIO_PREEMPT(0));
}
k_thread_priority_set(k_current_get(), old_prio);
}
Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>
1 file changed
