scheduler: Use precomputed time slice lengths

src/system/kernel/scheduler/scheduler.cpp

@@ -579,10 +579,9 @@ reschedule(int32 nextState)
 			bigtime_t quantum = nextThreadData->ComputeQuantum();
 			add_timer(quantumTimer, &reschedule_event, quantum,
 				B_ONE_SHOT_RELATIVE_TIMER);
-		} else {
+		} else
-			nextThreadData->StartQuantum();
 			gCurrentMode->rebalance_irqs(true);
-		}
+		nextThreadData->StartQuantum();
 
 		modeLocker.Unlock();
 		if (nextThread != oldThread)
@@ -674,6 +673,8 @@ scheduler_set_operation_mode(scheduler_mode mode)
 	gCurrentMode = sSchedulerModes[mode];
 	gCurrentMode->switch_to_mode();
 
+	ThreadData::ComputeQuantumLengths();
+
 	return B_OK;
 }
 

src/system/kernel/scheduler/scheduler_thread.cpp

@@ -9,6 +9,9 @@
 using namespace Scheduler;
 
 
+bigtime_t Scheduler::gQuantumLengths[THREAD_MAX_SET_PRIORITY + 1];
+
+
 ThreadData::ThreadData(Thread* thread)
 	:
 	fThread(thread)
@@ -116,12 +119,37 @@ ThreadData::ComputeQuantum()
 	quantum = std::max(quantum,	gCurrentMode->minimal_quantum);
 
 	fTimeLeft = quantum;
-	fQuantumStart = system_time();
 
 	return quantum;
 }
 
 
+/* static */ void
+ThreadData::ComputeQuantumLengths()
+{
+	for (int32 priority = 0; priority <= THREAD_MAX_SET_PRIORITY; priority++) {
+		const bigtime_t kQuantum0 = gCurrentMode->base_quantum;
+		if (priority >= B_URGENT_DISPLAY_PRIORITY) {
+			gQuantumLengths[priority] = kQuantum0;
+			continue;
+		}
+
+		const bigtime_t kQuantum1
+			= kQuantum0 * gCurrentMode->quantum_multipliers[0];
+		if (priority > B_NORMAL_PRIORITY) {
+			gQuantumLengths[priority] = _ScaleQuantum(kQuantum1, kQuantum0,
+				B_URGENT_DISPLAY_PRIORITY, B_NORMAL_PRIORITY, priority);
+			continue;
+		}
+
+		const bigtime_t kQuantum2
+			= kQuantum0 * gCurrentMode->quantum_multipliers[1];
+		gQuantumLengths[priority] = _ScaleQuantum(kQuantum2, kQuantum1,
+			B_NORMAL_PRIORITY, B_IDLE_PRIORITY, priority);
+	}
+}
+
+
 void
 ThreadData::_ComputeEffectivePriority() const
 {
@@ -181,23 +209,7 @@ ThreadData::_ChooseCPU(CoreEntry* core, bool& rescheduleNeeded) const
 inline bigtime_t
 ThreadData::_GetBaseQuantum() const
 {
-	int32 priority = GetEffectivePriority();
+	return gQuantumLengths[GetEffectivePriority()];
-
-	const bigtime_t kQuantum0 = gCurrentMode->base_quantum;
-	if (priority >= B_URGENT_DISPLAY_PRIORITY)
-		return kQuantum0;
-
-	const bigtime_t kQuantum1
-		= kQuantum0 * gCurrentMode->quantum_multipliers[0];
-	if (priority > B_NORMAL_PRIORITY) {
-		return _ScaleQuantum(kQuantum1, kQuantum0, B_URGENT_DISPLAY_PRIORITY,
-			B_NORMAL_PRIORITY, priority);
-	}
-
-	const bigtime_t kQuantum2
-		= kQuantum0 * gCurrentMode->quantum_multipliers[1];
-	return _ScaleQuantum(kQuantum2, kQuantum1, B_NORMAL_PRIORITY,
-		B_IDLE_PRIORITY, priority);
 }
 
 

src/system/kernel/scheduler/scheduler_thread.h

@@ -70,6 +70,7 @@ public:
 	inline	CoreEntry*	Core() const	{ return fCore; }
 	inline	void		UnassignCore() { fCore = NULL; }
 
+	static	void		ComputeQuantumLengths();
 private:
 	inline	int32		_GetPenalty() const;
 	inline	int32		_GetMinimalPriority() const;
@@ -118,6 +119,8 @@ public:
 	virtual	void		operator()(ThreadData* thread) = 0;
 };
 
+extern bigtime_t gQuantumLengths[THREAD_MAX_SET_PRIORITY + 1];
+
 
 inline bool
 ThreadData::HasCacheExpired() const