scheduler: Always update core heaps after thread migration

The main purpose of this patch is to eliminate the delay between thread
migration and result of that migration being visible in load statistics.
Such delay, in certain circumstances, may cause some cores to become
overloaded because the scheduler migrates too many threads to them before
the effect of migration becomes apparent.

src/system/kernel/scheduler/scheduler_cpu.cpp

@@ -527,7 +527,7 @@ CoreEntry::RemoveCPU(CPUEntry* cpu, ThreadProcessing& threadPostProcessing)
 
 
 void
-CoreEntry::_UpdateLoad()
+CoreEntry::_UpdateLoad(bool forceUpdate)
 {
 	SCHEDULER_ENTER_FUNCTION();
 
@@ -535,9 +535,11 @@ CoreEntry::_UpdateLoad()
 		return;
 
 	bigtime_t now = system_time();
-	if (now < kLoadMeasureInterval + fLastLoadUpdate)
+	bool intervalEnded = now >= kLoadMeasureInterval + fLastLoadUpdate;
+
+	if (!intervalEnded && !forceUpdate)
 		return;
-	WriteSpinLocker locker(fLoadLock);
+
 	WriteSpinLocker coreLocker(gCoreHeapsLock);
 
 	int32 newKey = GetLoad();
@@ -546,12 +548,16 @@ CoreEntry::_UpdateLoad()
 	ASSERT(oldKey >= 0);
 	ASSERT(newKey >= 0);
 
-	ASSERT(fCurrentLoad >= 0);
-	ASSERT(fLoad >= fCurrentLoad);
+	if (intervalEnded) {
+		WriteSpinLocker locker(fLoadLock);
 
-	fLoad = fCurrentLoad;
-	fLoadMeasurementEpoch++;
-	fLastLoadUpdate = now;
+		ASSERT(fCurrentLoad >= 0);
+		ASSERT(fLoad >= fCurrentLoad);
+
+		fLoad = fCurrentLoad;
+		fLoadMeasurementEpoch++;
+		fLastLoadUpdate = now;
+	}
 
 	if (oldKey == newKey)
 		return;

src/system/kernel/scheduler/scheduler_cpu.h

@@ -173,7 +173,7 @@ public:
 	static inline		CoreEntry*		GetCore(int32 cpu);
 
 private:
-						void			_UpdateLoad();
+						void			_UpdateLoad(bool forceUpdate = false);
 
 	static				void			_UnassignThread(Thread* thread,
 											void* core);
@@ -416,7 +416,7 @@ CoreEntry::AddLoad(int32 load, uint32 epoch, bool updateLoad)
 	locker.Unlock();
 
 	if (updateLoad)
-		_UpdateLoad();
+		_UpdateLoad(true);
 }
 
 
@@ -434,7 +434,7 @@ CoreEntry::RemoveLoad(int32 load, bool force)
 		atomic_add(&fLoad, -load);
 		locker.Unlock();
 
-		_UpdateLoad();
+		_UpdateLoad(true);
 	}
 	return fLoadMeasurementEpoch;
 }