hw: schedule on demand (Fix #3157)

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

@@ -164,22 +164,20 @@ bool Cpu::interrupt(unsigned const irq_id)
 Cpu_job & Cpu::schedule()
 {
 	/* update scheduler */
-	time_t quota = _timer.update_time();
 	Job & old_job = scheduled_job();
 	old_job.exception(*this);
-	_timer.process_timeouts();
-	_scheduler.update(quota);
 
-	/* get new job */
-	Job & new_job = scheduled_job();
-	quota = _scheduler.head_quota();
-
-	_timer.set_timeout(this, quota);
-
-	_timer.schedule_timeout();
+	if (_scheduler.need_to_schedule()) {
+		time_t quota = _timer.update_time();
+		_timer.process_timeouts();
+		_scheduler.update(quota);
+		quota = _scheduler.head_quota();
+		_timer.set_timeout(this, quota);
+		_timer.schedule_timeout();
+	}
 
 	/* return new job */
-	return new_job;
+	return scheduled_job();
 }
 
 
@@ -195,9 +193,9 @@ addr_t Cpu::stack_start() {
 Cpu::Cpu(unsigned const id, Pic & pic,
          Inter_processor_work_list & global_work_list)
 :
-	_id(id), _pic(pic), _timer(_id),
+	_id(id), _pic(pic), _timer(*this),
 	_scheduler(&_idle, _quota(), _fill()), _idle(*this),
-	_ipi_irq(*this), _timer_irq(_timer.interrupt_id(), *this),
+	_ipi_irq(*this),
 	_global_work_list(global_work_list)
 { _arch_init(); }
 

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

@@ -116,7 +116,6 @@ class Kernel::Cpu : public Genode::Cpu, private Irq::Pool, private Timeout
 		Cpu_scheduler  _scheduler;
 		Idle_thread    _idle;
 		Ipi            _ipi_irq;
-		Irq            _timer_irq; /* timer IRQ implemented as empty event */
 
 		Inter_processor_work_list &_global_work_list;
 		Inter_processor_work_list  _local_work_list {};

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

@@ -101,7 +101,7 @@ unsigned Cpu_scheduler::_trim_consumption(unsigned & q)
 {
 	q = Genode::min(Genode::min(q, _head_quota), _residual);
 	if (!_head_yields) { return _head_quota - q; }
-	_head_yields = 0;
+	_head_yields = false;
 	return 0;
 }
 
@@ -129,6 +129,8 @@ void Cpu_scheduler::_quota_adaption(Share * const s, unsigned const q)
 
 void Cpu_scheduler::update(unsigned q)
 {
+	_need_to_schedule = false;
+
 	/* do not detract the quota if the head context was removed even now */
 	if (_head) {
 		unsigned const r = _trim_consumption(q);
@@ -148,12 +150,21 @@ bool Cpu_scheduler::ready_check(Share * const s1)
 	assert(_head);
 
 	ready(s1);
+
+	if (_need_to_schedule) return _need_to_schedule;
+
 	Share * s2 = _head;
-	if (!s1->_claim) { return s2 == _idle; }
-	if (!_head_claims) { return 1; }
-	if (s1->_prio != s2->_prio) { return s1->_prio > s2->_prio; }
-	for (; s2 && s2 != s1; s2 = _share(Claim_list::next(s2))) ;
-	return !s2;
+	if (!s1->_claim) {
+		_need_to_schedule = s2 == _idle;
+	} else if (!_head_claims) {
+		_need_to_schedule = true;
+	} else if (s1->_prio != s2->_prio) {
+		_need_to_schedule = s1->_prio > s2->_prio;
+	} else {
+		for (; s2 && s2 != s1; s2 = _share(Claim_list::next(s2))) ;
+		_need_to_schedule = !s2;
+	}
+	return _need_to_schedule;
 }
 
 
@@ -161,6 +172,8 @@ void Cpu_scheduler::ready(Share * const s)
 {
 	assert(!s->_ready && s != _idle);
 
+	_need_to_schedule = true;
+
 	s->_ready = 1;
 	s->_fill = _fill;
 	_fills.insert_tail(s);
@@ -174,6 +187,9 @@ void Cpu_scheduler::ready(Share * const s)
 void Cpu_scheduler::unready(Share * const s)
 {
 	assert(s->_ready && s != _idle);
+
+	_need_to_schedule = true;
+
 	s->_ready = 0;
 	_fills.remove(s);
 	if (!s->_quota) { return; }
@@ -182,13 +198,18 @@ void Cpu_scheduler::unready(Share * const s)
 }
 
 
-void Cpu_scheduler::yield() { _head_yields = 1; }
+void Cpu_scheduler::yield()
+{
+	_head_yields = true;
+	_need_to_schedule = true;
+}
 
 
 void Cpu_scheduler::remove(Share * const s)
 {
 	assert(s != _idle);
 
+	_need_to_schedule = true;
 	if (s == _head) _head = nullptr;
 	if (s->_ready) { _fills.remove(s); }
 	if (!s->_quota) { return; }
@@ -200,6 +221,7 @@ void Cpu_scheduler::remove(Share * const s)
 void Cpu_scheduler::insert(Share * const s)
 {
 	assert(!s->_ready);
+	_need_to_schedule = true;
 	if (!s->_quota) { return; }
 	s->_claim = s->_quota;
 	_ucl[s->_prio].insert_head(s);
@@ -217,5 +239,5 @@ void Cpu_scheduler::quota(Share * const s, unsigned const q)
 
 Cpu_scheduler::Cpu_scheduler(Share * const i, unsigned const q,
                              unsigned const f)
-: _idle(i), _head_yields(0), _quota(q), _residual(q), _fill(f)
+: _idle(i), _quota(q), _residual(q), _fill(f)
 { _set_head(i, f, 0); }

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

@@ -128,10 +128,11 @@ class Kernel::Cpu_scheduler
 		Share *        _head = nullptr;
 		unsigned       _head_quota  = 0;
 		bool           _head_claims = false;
-		bool           _head_yields;
+		bool           _head_yields = false;
 		unsigned const _quota;
 		unsigned       _residual;
 		unsigned const _fill;
+		bool           _need_to_schedule { true };
 
 		template <typename F> void _for_each_prio(F f) {
 			for (signed p = Prio::MAX; p > Prio::MIN - 1; p--) { f(p); } }
@@ -179,6 +180,9 @@ class Kernel::Cpu_scheduler
 		 */
 		Cpu_scheduler(Share * const i, unsigned const q, unsigned const f);
 
+		bool need_to_schedule() { return _need_to_schedule; }
+		void timeout()          { _need_to_schedule = true; }
+
 		/**
 		 * Update head according to the consumption of quota 'q'
 		 */

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

@@ -12,6 +12,7 @@
  */
 
 /* Core includes */
+#include <kernel/cpu.h>
 #include <kernel/timer.h>
 #include <kernel/configuration.h>
 #include <hw/assert.h>
@@ -19,6 +20,13 @@
 using namespace Kernel;
 
 
+void Timer::Irq::occurred() { _cpu.scheduler().timeout(); }
+
+
+Timer::Irq::Irq(unsigned id, Cpu &cpu)
+: Kernel::Irq(id, cpu.irq_pool()), _cpu(cpu) {}
+
+
 time_t Timer::timeout_age_us(Timeout const * const timeout) const
 {
 	time_t const age = (time_t)_time - timeout->_start;
@@ -131,7 +139,8 @@ void Timer::process_timeouts()
 }
 
 
-Timer::Timer(unsigned cpu_id) : _cpu_id(cpu_id), _driver(cpu_id)
+Timer::Timer(Cpu & cpu)
+: _driver(cpu.id()), _irq(interrupt_id(), cpu)
 {
 	/*
 	 * The timer frequency should allow a good accuracy on the smallest

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

@@ -16,6 +16,7 @@
 
 /* base-hw includes */
 #include <kernel/types.h>
+#include <kernel/irq.h>
 
 /* Genode includes */
 #include <util/list.h>
@@ -25,6 +26,7 @@
 
 namespace Kernel
 {
+	class Cpu;
 	class Timeout;
 	class Timer;
 }
@@ -61,10 +63,23 @@ class Kernel::Timer
 {
 	private:
 
+		class Irq : private Kernel::Irq
+		{
+			private:
+
+				Cpu & _cpu;
+
+			public:
+
+				Irq(unsigned id, Cpu & cpu);
+
+				void occurred() override;
+		};
+
 		using Driver = Timer_driver;
 
-		unsigned const        _cpu_id;
 		Driver                _driver;
+		Irq                   _irq;
 		time_t                _time = 0;
 		bool                  _time_period = false;
 		Genode::List<Timeout> _timeout_list[2];
@@ -82,11 +97,12 @@ class Kernel::Timer
 
 	public:
 
-		Timer(unsigned cpu_id);
+		Timer(Cpu & cpu);
 
 		void schedule_timeout();
 
 		time_t update_time();
+
 		void process_timeouts();
 
 		void set_timeout(Timeout * const timeout, time_t const duration);

repos/base-hw/src/core/spec/riscv/kernel/thread.cc

@@ -21,12 +21,15 @@ using namespace Kernel;
 void Thread::Pd_update::execute() {}
 
 
-void Thread::exception(Cpu&)
+void Thread::exception(Cpu & cpu)
 {
 	using Context = Genode::Cpu::Context;
 
-	if (regs->is_irq())
+	if (regs->is_irq()) {
+		/* there are only cpu-local timer interrupts right now */
+		cpu.interrupt(5);
 		return;
+	}
 
 	switch(regs->cpu_exception) {
 	case Context::ECALL_FROM_USER: