hw: merge booleans in scheduler into one state

Instead of having `_yield` and `_need_to_schedule` booleans, use one
consistent state variable.

Ref genodelabs/genode#5115

repos/base-hw/src/core/kernel/cpu_scheduler.cc

@@ -70,7 +70,7 @@ void Cpu_scheduler::_current_claimed(unsigned const r)
 	 * at least ensure that it does not have to wait for all unprioritized
 	 * scheduling contexts as well before being scheduled again.
 	 */
-	if (!_yield)
+	if (_state != YIELD)
 		_fills.to_head(&_current->_fill_item);
 }
 
@@ -123,7 +123,7 @@ bool Cpu_scheduler::_schedule_fill()
 unsigned Cpu_scheduler::_trim_consumption(unsigned &q)
 {
 	q = Genode::min(Genode::min(q, _current_quantum), _super_period_left);
-	if (!_yield)
+	if (_state != YIELD)
 		return _current_quantum - q;
 
 	return 0;
@@ -157,7 +157,6 @@ void Cpu_scheduler::update(time_t time)
 
 	unsigned duration = (unsigned) (time - _last_time);
 	_last_time        = time;
-	_need_to_schedule = false;
 	unsigned const r  = _trim_consumption(duration);
 
 	/* do not detract the quota if the current share was removed even now */
@@ -166,9 +165,10 @@ void Cpu_scheduler::update(time_t time)
 		else                  _current_filled(r);
 	}
 
-	_yield = false;
 	_consumed(duration);
 
+	_state = UP_TO_DATE;
+
 	if (_schedule_claim())
 		return;
 
@@ -184,6 +184,9 @@ void Cpu_scheduler::ready(Share &s)
 	assert(!s._ready && &s != &_idle);
 
 	s._ready = true;
+
+	bool out_of_date = false;
+
 	if (s._quota) {
 
 		_ucl[s._prio].remove(&s._claim_item);
@@ -192,12 +195,9 @@ void Cpu_scheduler::ready(Share &s)
 			_rcl[s._prio].insert_head(&s._claim_item);
 			if (_current && _current->_claim) {
 
-				if (s._prio >= _current->_prio)
+				if (s._prio >= _current->_prio) out_of_date = true;
-					_need_to_schedule = true;
+			} else out_of_date = true;
-			} else
-				_need_to_schedule = true;
 		} else {
-
 			_rcl[s._prio].insert_tail(&s._claim_item);;
 		}
 	}
@@ -205,7 +205,9 @@ void Cpu_scheduler::ready(Share &s)
 	s._fill = _fill;
 	_fills.insert_tail(&s._fill_item);
 
-	if (!_current || _current == &_idle) _need_to_schedule = true;
+	if (!_current || _current == &_idle) out_of_date = true;
+
+	if (out_of_date && _state == UP_TO_DATE) _state = OUT_OF_DATE;
 }
 
 
@@ -213,8 +215,7 @@ void Cpu_scheduler::unready(Share &s)
 {
 	assert(s._ready && &s != &_idle);
 
-	if (&s == _current)
+	if (&s == _current && _state == UP_TO_DATE) _state = OUT_OF_DATE;
-		_need_to_schedule = true;
 
 	s._ready = false;
 	_fills.remove(&s._fill_item);
@@ -229,8 +230,7 @@ void Cpu_scheduler::unready(Share &s)
 
 void Cpu_scheduler::yield()
 {
-	_yield = true;
+	_state = YIELD;
-	_need_to_schedule = true;
 }
 
 

repos/base-hw/src/core/kernel/cpu_scheduler.h

@@ -198,17 +198,18 @@ class Kernel::Cpu_scheduler
 		typedef Cpu_share    Share;
 		typedef Cpu_priority Prio;
 
+		enum State { UP_TO_DATE, OUT_OF_DATE, YIELD };
+
+		State          _state { UP_TO_DATE };
 		Share_list     _rcl[Prio::max() + 1]; /* ready claims */
 		Share_list     _ucl[Prio::max() + 1]; /* unready claims */
 		Share_list     _fills { };          /* ready fills */
 		Share         &_idle;
 		Share         *_current = nullptr;
 		unsigned       _current_quantum { 0 };
-		bool           _yield = false;
 		unsigned const _super_period_length;
 		unsigned       _super_period_left { _super_period_length };
 		unsigned const _fill;
-		bool           _need_to_schedule { true };
 		time_t         _last_time { 0 };
 
 		template <typename F> void _for_each_prio(F f)
@@ -260,8 +261,10 @@ class Kernel::Cpu_scheduler
 		 */
 		Cpu_scheduler(Share &i, unsigned const q, unsigned const f);
 
-		bool need_to_schedule() { return _need_to_schedule; }
+		bool need_to_schedule() const { return _state != UP_TO_DATE; }
-		void timeout()          { _need_to_schedule = true; }
+
+		void timeout() {
+			if (_state == UP_TO_DATE) _state = OUT_OF_DATE; }
 
 		/**
 		 * Update state according to the current (absolute) time

repos/base-hw/src/test/cpu_scheduler/main.cc

@@ -265,13 +265,13 @@ void Cpu_scheduler_test::Cpu_scheduler::print(Output &output) const
 	print(output, "(\n");
 	print(output, "   quota: ", _super_period_left, "/", _super_period_length, ", ");
 	print(output, "fill: ", _fill, ", ");
-	print(output, "need to schedule: ", _need_to_schedule ? "true" : "false", ", ");
+	print(output, "need to schedule: ", need_to_schedule() ? "true" : "false", ", ");
 	print(output, "last_time: ", _last_time);
 
 	if (_current != nullptr) {
 
 		print(output, "\n   current: ( ");
-		if (_need_to_schedule) {
+		if (need_to_schedule()) {
 			print(output, "\033[31m");
 		} else {
 			print(output, "\033[32m");
@@ -280,7 +280,7 @@ void Cpu_scheduler_test::Cpu_scheduler::print(Output &output) const
 		print(output, "quota: ", _current_quantum, ", ");
 		print(output, "\033[0m");
 		print(output, "claims: ", (_current && _current->_claim) ? "true" : "false", ", ");
-		print(output, "yields: ", _yield ? "true" : "false", " ");
+		print(output, "yields: ", _state == YIELD ? "true" : "false", " ");
 		print(output, ")");
 	}
 	bool prios_empty { true };
@@ -303,7 +303,7 @@ void Cpu_scheduler_test::Cpu_scheduler::print(Output &output) const
 					_rcl[prio].for_each([&] (Kernel::Cpu_share const &share) {
 
 						if (&share == _current && _current->_claim) {
-							if (_need_to_schedule) {
+							if (need_to_schedule()) {
 								print(output, "\033[31m");
 							} else {
 								print(output, "\033[32m");
@@ -343,7 +343,7 @@ void Cpu_scheduler_test::Cpu_scheduler::print(Output &output) const
 		_fills.for_each([&] (Kernel::Cpu_share const &share) {
 
 			if (&share == _current && !_current->_claim) {
-				if (_need_to_schedule) {
+				if (need_to_schedule()) {
 					print(output, "\033[31m");
 				} else {
 					print(output, "\033[32m");