Commit cb3964f0 authored by Andy Ross's avatar Andy Ross Committed by Anas Nashif
Browse files

kernel/sched: Reset time slice on swap in SMP 



In uniprocessor mode, the kernel knows when a context switch "is
coming" because of the cache optimization and can use that to do
things like update time slice state.  But on SMP the scheduler state
may be updated on the other CPU at any time, so we don't know that a
switch is going to happen until the last minute.

Expose reset_time_slice() as a public function and call it when needed
out of z_swap().

Signed-off-by: default avatarAndy Ross <andrew.j.ross@intel.com>
parent d4429276

kernel/include/ksched.h

+1 −0
Original line number Diff line number Diff line
@@ -57,6 +57,7 @@ struct k_thread *z_find_first_thread_to_unpend(_wait_q_t *wait_q, 
					      struct k_thread *from);

void idle(void *a, void *b, void *c);

void z_time_slice(int ticks);

void z_reset_time_slice(void);

void z_sched_abort(struct k_thread *thread);

void z_sched_ipi(void);

kernel/include/kswap.h

+4 −0
Original line number Diff line number Diff line
@@ -64,6 +64,10 @@ static ALWAYS_INLINE unsigned int do_swap(unsigned int key, 
	new_thread = z_get_next_ready_thread();



	if (new_thread != old_thread) {

#ifdef CONFIG_TIMESLICING

		z_reset_time_slice();

#endif



		old_thread->swap_retval = -EAGAIN;



#ifdef CONFIG_SMP

kernel/sched.c

+13 −9
Original line number Diff line number Diff line
@@ -249,7 +249,7 @@ static int slice_max_prio; 
static struct k_thread *pending_current;

#endif



static void reset_time_slice(void)

void z_reset_time_slice(void)

{

	/* Add the elapsed time since the last announced tick to the

	 * slice count, as we'll see those "expired" ticks arrive in a
@@ -267,7 +267,7 @@ void k_sched_time_slice_set(s32_t slice, int prio) 
		_current_cpu->slice_ticks = 0;

		slice_time = z_ms_to_ticks(slice);

		slice_max_prio = prio;

		reset_time_slice();

		z_reset_time_slice();

	}

}
@@ -284,7 +284,7 @@ void z_time_slice(int ticks) 
{

#ifdef CONFIG_SWAP_NONATOMIC

	if (pending_current == _current) {

		reset_time_slice();

		z_reset_time_slice();

		return;

	}

	pending_current = NULL;
@@ -293,7 +293,7 @@ void z_time_slice(int ticks) 
	if (slice_time && sliceable(_current)) {

		if (ticks >= _current_cpu->slice_ticks) {

			z_move_thread_to_end_of_prio_q(_current);

			reset_time_slice();

			z_reset_time_slice();

		} else {

			_current_cpu->slice_ticks -= ticks;

		}
@@ -301,8 +301,6 @@ void z_time_slice(int ticks) 
		_current_cpu->slice_ticks = 0;

	}

}

#else

static void reset_time_slice(void) { /* !CONFIG_TIMESLICING */ }

#endif



static void update_cache(int preempt_ok)
@@ -311,9 +309,11 @@ static void update_cache(int preempt_ok) 
	struct k_thread *th = next_up();



	if (should_preempt(th, preempt_ok)) {

#ifdef CONFIG_TIMESLICING

		if (th != _current) {

			reset_time_slice();

			z_reset_time_slice();

		}

#endif

		_kernel.ready_q.cache = th;

	} else {

		_kernel.ready_q.cache = _current;
@@ -342,7 +342,9 @@ void z_add_thread_to_ready_q(struct k_thread *thread) 
void z_move_thread_to_end_of_prio_q(struct k_thread *thread)

{

	LOCKED(&sched_spinlock) {

		if (z_is_thread_queued(thread)) {

			_priq_run_remove(&_kernel.ready_q.runq, thread);

		}

		_priq_run_add(&_kernel.ready_q.runq, thread);

		z_mark_thread_as_queued(thread);

		update_cache(thread == _current);
@@ -609,7 +611,9 @@ void *z_get_next_switch_handle(void *interrupted) 
		struct k_thread *th = next_up();



		if (_current != th) {

			reset_time_slice();

#ifdef CONFIG_TIMESLICING

			z_reset_time_slice();

#endif

			_current_cpu->swap_ok = 0;

			set_current(th);

#ifdef SPIN_VALIDATE

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