hw: fix bug in scheduler timing

By now the scheduling timer was only refreshed for a new scheduling timeout
when the choosen scheduling context has changed. But we want it to be refreshed
also when the scheduled context yields without an effect to the schedulers
choice (this is the case e.g. when the idle thread gets a scheduling timeout
or a thread yields without any competitor in its priority band).

ref #1151

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

@@ -74,25 +74,6 @@ namespace Kernel
 	Signal_context_pool * signal_context_pool() { return unmanaged_singleton<Signal_context_pool>(); }
 	Signal_receiver_pool * signal_receiver_pool() { return unmanaged_singleton<Signal_receiver_pool>(); }
 
-	/**
-	 * Return singleton kernel-timer
-	 */
-	Timer * timer()
-	{
-		static Timer _object;
-		return &_object;
-	}
-
-	/**
-	 * Start a new scheduling lap
-	 */
-	void reset_scheduling_time(unsigned const processor_id)
-	{
-		unsigned const tics = timer()->ms_to_tics(USER_LAP_TIME_MS);
-		timer()->start_one_shot(tics, processor_id);
-	}
-
-
 	/**
 	 * Static kernel PD that describes core
 	 */
@@ -287,9 +268,13 @@ extern "C" void init_kernel_multiprocessor()
 	 */
 	perf_counter()->enable();
 
-	/* initialize interrupt controller */
+	/* locally initialize processor */
-	pic()->init_processor_local();
 	unsigned const processor_id = Processor::executing_id();
+	Processor * const processor = processor_pool()->processor(processor_id);
+	processor->init_processor_local();
+
+	/* locally initialize interrupt controller */
+	pic()->init_processor_local();
 	pic()->unmask(Timer::interrupt_id(processor_id), processor_id);
 
 	/* as primary processor create the core main thread */
@@ -315,7 +300,7 @@ extern "C" void init_kernel_multiprocessor()
 		_main_thread_utcb->start_info()->init(t.id(), Genode::Native_capability());
 		t.ip = (addr_t)CORE_MAIN;;
 		t.sp = (addr_t)s + STACK_SIZE;
-		t.init(processor_pool()->processor(processor_id), core_pd(), &utcb, 1);
+		t.init(processor, core_pd(), &utcb, 1);
 
 		/* initialize interrupt objects */
 		static Genode::uint8_t _irqs[Pic::MAX_INTERRUPT_ID * sizeof(Irq)];
@@ -326,7 +311,6 @@ extern "C" void init_kernel_multiprocessor()
 		/* kernel initialization finished */
 		Genode::printf("kernel initialized\n");
 	}
-	reset_scheduling_time(processor_id);
 }
 
 
@@ -338,31 +322,10 @@ extern "C" void kernel()
 	/* ensure that no other processor accesses kernel data while we do */
 	data_lock().lock();
 
-	/* determine local processor scheduler */
+	/* determine local processor object and let it handle its exception */
 	unsigned const processor_id = Processor::executing_id();
 	Processor * const processor = processor_pool()->processor(processor_id);
-	Scheduler<Processor_client> * const scheduler = processor->scheduler();
+	processor->exception();
-
-	/*
-	 * Request the current processor occupant without any update. While this
-	 * processor was outside the kernel, another processor may have changed the
-	 * scheduling of the local activities in a way that an update would return
-	 * an occupant other than that whose exception caused the kernel entry.
-	 */
-	Processor_client * const old_client = scheduler->occupant();
-	Processor_lazy_state * const old_state = old_client->lazy_state();
-	old_client->exception(processor_id);
-
-	/*
-	 * The processor local as well as remote exception-handling may have
-	 * changed the scheduling of the local activities. Hence we must update the
-	 * processor occupant.
-	 */
-	Processor_client * const new_client = scheduler->update_occupant();
-	Processor_lazy_state * const new_state = new_client->lazy_state();
-	if (old_client != new_client) { reset_scheduling_time(processor_id); }
-	processor->prepare_proceeding(old_state, new_state);
-	new_client->proceed(processor_id);
 }
 
 

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

@@ -44,16 +44,13 @@ void Kernel::Processor_client::_interrupt(unsigned const processor_id)
 	/* determine handling for specific interrupt */
 	unsigned irq_id;
 	Pic * const ic = pic();
-	if (ic->take_request(irq_id))
+	if (ic->take_request(irq_id)) {
-	{
-		/* check wether the interrupt is a processor-scheduling timeout */
-		if (timer()->interrupt_id(processor_id) == irq_id) {
 
-			_processor->scheduler()->yield_occupation();
+		/* check wether the interrupt is a processor-scheduling timeout */
-			timer()->clear_interrupt(processor_id);
+		if (!_processor->check_timer_interrupt(irq_id)) {
 
 			/* check wether the interrupt is our inter-processor interrupt */
-		} else if (ic->is_ip_interrupt(irq_id, processor_id)) {
+			if (ic->is_ip_interrupt(irq_id, processor_id)) {
 
 				_processor->ip_interrupt();
 
@@ -64,6 +61,7 @@ void Kernel::Processor_client::_interrupt(unsigned const processor_id)
 				Irq::occurred(irq_id);
 			}
 		}
+	}
 	/* end interrupt request at controller */
 	ic->finish_request();
 }

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

@@ -16,6 +16,7 @@
 #define _KERNEL__PROCESSOR_H_
 
 /* core includes */
+#include <timer.h>
 #include <processor_driver.h>
 #include <kernel/scheduler.h>
 
@@ -142,6 +143,16 @@ class Kernel::Processor : public Processor_driver
 		unsigned const      _id;
 		Processor_scheduler _scheduler;
 		bool                _ip_interrupt_pending;
+		Timer * const       _timer;
+
+		/**
+		 * Reset the scheduling timer for a new scheduling interval
+		 */
+		void _reset_timer()
+		{
+			unsigned const tics = _timer->ms_to_tics(USER_LAP_TIME_MS);
+			_timer->start_one_shot(tics, _id);
+		}
 
 	public:
 
@@ -150,12 +161,35 @@ class Kernel::Processor : public Processor_driver
 		 *
 		 * \param id           kernel name of the processor object
 		 * \param idle_client  client that gets scheduled on idle
+		 * \param timer        timer that is used for scheduling the processor
 		 */
-		Processor(unsigned const id, Processor_client * const idle_client)
+		Processor(unsigned const id, Processor_client * const idle_client,
+		          Timer * const timer)
 		:
-			_id(id), _scheduler(idle_client), _ip_interrupt_pending(false)
+			_id(id), _scheduler(idle_client), _ip_interrupt_pending(false),
+			_timer(timer)
 		{ }
 
+		/**
+		 * Initializate on the processor that this object corresponds to
+		 */
+		void init_processor_local() { _reset_timer(); }
+
+		/**
+		 * Check for a scheduling timeout and handle it in case
+		 *
+		 * \param interrupt_id  kernel name of interrupt that caused this call
+		 *
+		 * \return  wether it was a timeout and therefore has been handled
+		 */
+		bool check_timer_interrupt(unsigned const interrupt_id)
+		{
+			if (_timer->interrupt_id(_id) != interrupt_id) { return false; }
+			_scheduler.yield_occupation();
+			_timer->clear_interrupt(_id);
+			return true;
+		}
+
 		/**
 		 * Perform outstanding TLB maintainance work
 		 */
@@ -183,6 +217,33 @@ class Kernel::Processor : public Processor_driver
 		 */
 		void schedule(Processor_client * const client);
 
+		/**
+		 * Handle exception of the processor and proceed its user execution
+		 */
+		void exception()
+		{
+			/*
+			 * Request the current occupant without any update. While the
+			 * processor was outside the kernel, another processor may have changed the
+			 * scheduling of the local activities in a way that an update would return
+			 * an occupant other than that whose exception caused the kernel entry.
+			 */
+			Processor_client * const old_client = _scheduler.occupant();
+			Processor_lazy_state * const old_state = old_client->lazy_state();
+			old_client->exception(_id);
+
+			/*
+			 * The processor local as well as remote exception-handling may have
+			 * changed the scheduling of the local activities. Hence we must update the
+			 * occupant.
+			 */
+			bool update;
+			Processor_client * const new_client = _scheduler.update_occupant(update);
+			if (update) { _reset_timer(); }
+			Processor_lazy_state * const new_state = new_client->lazy_state();
+			prepare_proceeding(old_state, new_state);
+			new_client->proceed(_id);
+		}
 
 		/***************
 		 ** Accessors **

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

@@ -80,6 +80,7 @@ class Kernel::Processor_pool
 {
 	private:
 
+		Timer _timer;
 		char  _processors[PROCESSORS][sizeof(Processor)];
 		char  _idle_threads[PROCESSORS][sizeof(Idle_thread)];
 
@@ -103,7 +104,7 @@ class Kernel::Processor_pool
 		{
 			for (unsigned i = 0; i < PROCESSORS; i++) {
 				new (_idle_threads[i]) Idle_thread(processor(i));
-				new (_processors[i]) Processor(i, _idle_thread(i));
+				new (_processors[i]) Processor(i, _idle_thread(i), &_timer);
 			}
 		}
 

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

@@ -232,11 +232,22 @@ class Kernel::Scheduler_item : public Double_list<T>::Item
 template <typename T>
 class Kernel::Scheduler
 {
-	protected:
+	private:
 
 		T * const      _idle;
 		T *            _occupant;
 		Double_list<T> _items[Priority::MAX + 1];
+		bool           _yield;
+
+		bool _check_update(T * const occupant)
+		{
+			if (_yield) {
+				_yield = false;
+				return true;
+			}
+			if (_occupant != occupant) { return true; }
+			return false;
+		}
 
 	public:
 
@@ -252,12 +263,17 @@ class Kernel::Scheduler
 		 *
 		 * \return  updated occupant reference
 		 */
-		T * update_occupant()
+		T * update_occupant(bool & update)
 		{
 			for (int i = Priority::MAX; i >= 0 ; i--) {
-				_occupant = _items[i].head();
+				T * const head = _items[i].head();
-				if (_occupant) { return _occupant; }
+				if (!head) { continue; }
+				update = _check_update(head);
+				_occupant = head;
+				return head;
 			}
+			update = _check_update(_idle);
+			_occupant = 0;
 			return _idle;
 		}
 
@@ -266,6 +282,7 @@ class Kernel::Scheduler
 		 */
 		void yield_occupation()
 		{
+			_yield = true;
 			if (!_occupant) { return; }
 			_items[_occupant->priority()].head_to_tail();
 		}