diff --git a/src/system/kernel/scheduler/low_latency.cpp b/src/system/kernel/scheduler/low_latency.cpp
index 073c07b040..3635bee7ab 100644
--- a/src/system/kernel/scheduler/low_latency.cpp
+++ b/src/system/kernel/scheduler/low_latency.cpp
@@ -57,15 +57,13 @@ choose_core(const ThreadData* threadData)
 
 	int32 index = 0;
 	CPUSet mask = threadData->GetCPUMask();
-	if (mask.IsEmpty()) {
-		// ignore when empty
-		mask.SetAll();
-	}
+	const bool useMask = !mask.IsEmpty();
+
 	CoreEntry* core = NULL;
 	if (package != NULL) {
 		do {
 			core = package->GetIdleCore(index++);
-		} while (core != NULL && !core->CPUMask().Matches(mask));
+		} while (useMask && core != NULL && !core->CPUMask().Matches(mask));
 	}
 	if (core == NULL) {
 		ReadSpinLocker coreLocker(gCoreHeapsLock);
@@ -73,12 +71,12 @@ choose_core(const ThreadData* threadData)
 		// no idle cores, use least occupied core
 		do {
 			core = gCoreLoadHeap.PeekMinimum(index++);
-		} while (core != NULL && !core->CPUMask().Matches(mask));
+		} while (useMask && core != NULL && !core->CPUMask().Matches(mask));
 		if (core == NULL) {
 			index = 0;
 			do {
 				core = gCoreHighLoadHeap.PeekMinimum(index++);
-			} while (core != NULL && !core->CPUMask().Matches(mask));
+			} while (useMask && core != NULL && !core->CPUMask().Matches(mask));
 		}
 	}
 
@@ -98,23 +96,21 @@ rebalance(const ThreadData* threadData)
 	// Get the least loaded core.
 	ReadSpinLocker coreLocker(gCoreHeapsLock);
 	CPUSet mask = threadData->GetCPUMask();
-	if (mask.IsEmpty()) {
-		// ignore when empty
-		mask.SetAll();
-	}
+	const bool useMask = !mask.IsEmpty();
+
 	int32 index = 0;
 	CoreEntry* other;
 	do {
 		other = gCoreLoadHeap.PeekMinimum(index++);
-		if (other != NULL && other->CPUMask().IsEmpty())
+		if (other != NULL && (useMask && other->CPUMask().IsEmpty()))
 			panic("other->CPUMask().IsEmpty()\n");
-	} while (other != NULL && !other->CPUMask().Matches(mask));
+	} while (useMask && other != NULL && !other->CPUMask().Matches(mask));
 
 	if (other == NULL) {
 		index = 0;
 		do {
 			other = gCoreHighLoadHeap.PeekMinimum(index++);
-		} while (other != NULL && !other->CPUMask().Matches(mask));
+		} while (useMask && other != NULL && !other->CPUMask().Matches(mask));
 	}
 	coreLocker.Unlock();
 	ASSERT(other != NULL);
diff --git a/src/system/kernel/scheduler/power_saving.cpp b/src/system/kernel/scheduler/power_saving.cpp
index 5b98573964..4ebd746d37 100644
--- a/src/system/kernel/scheduler/power_saving.cpp
+++ b/src/system/kernel/scheduler/power_saving.cpp
@@ -89,14 +89,11 @@ choose_core(const ThreadData* threadData)
 	CoreEntry* core = NULL;
 
 	CPUSet mask = threadData->GetCPUMask();
-	if (mask.IsEmpty()) {
-		// ignore when empty
-		mask.SetAll();
-	}
+	const bool useMask = !mask.IsEmpty();
 
 	// try to pack all threads on one core
 	core = choose_small_task_core();
-	if (core != NULL && !core->CPUMask().Matches(mask))
+	if (core != NULL && (useMask && !core->CPUMask().Matches(mask)))
 		core = NULL;
 
 	if (core == NULL || core->GetLoad() + threadData->GetLoad() >= kHighLoad) {
@@ -106,12 +103,12 @@ choose_core(const ThreadData* threadData)
 		int32 index = 0;
 		do {
 			core = gCoreLoadHeap.PeekMinimum(index++);
-		} while (core != NULL && !core->CPUMask().Matches(mask));
+		} while (useMask && core != NULL && !core->CPUMask().Matches(mask));
 		if (core == NULL) {
 			coreLocker.Unlock();
 
 			core = choose_idle_core();
-			if (!core->CPUMask().Matches(mask))
+			if (useMask && !core->CPUMask().Matches(mask))
 				core = NULL;
 
 			if (core == NULL) {
@@ -119,7 +116,7 @@ choose_core(const ThreadData* threadData)
 				index = 0;
 				do {
 					core = gCoreHighLoadHeap.PeekMinimum(index++);
-				} while (core != NULL && !core->CPUMask().Matches(mask));
+				} while (useMask && core != NULL && !core->CPUMask().Matches(mask));
 			}
 		}
 	}
@@ -137,10 +134,8 @@ rebalance(const ThreadData* threadData)
 	ASSERT(!gSingleCore);
 
 	CPUSet mask = threadData->GetCPUMask();
-	if (mask.IsEmpty()) {
-		// ignore when empty
-		mask.SetAll();
-	}
+	const bool useMask = !mask.IsEmpty();
+
 	CoreEntry* core = threadData->Core();
 
 	int32 coreLoad = core->GetLoad();
@@ -151,7 +146,7 @@ rebalance(const ThreadData* threadData)
 			CoreEntry* smallTaskCore = choose_small_task_core();
 
 			if (threadLoad > coreLoad / 3 || smallTaskCore == NULL
-				|| !smallTaskCore->CPUMask().Matches(mask)) {
+					|| (useMask && !smallTaskCore->CPUMask().Matches(mask))) {
 				return core;
 			}
 			return coreLoad > kVeryHighLoad ? smallTaskCore : core;
@@ -165,12 +160,12 @@ rebalance(const ThreadData* threadData)
 		int32 index = 0;
 		do {
 			other = gCoreLoadHeap.PeekMaximum(index++);
-		} while (other != NULL && !core->CPUMask().Matches(mask));
+		} while (useMask && other != NULL && !other->CPUMask().Matches(mask));
 		if (other == NULL) {
 			index = 0;
 			do {
 				other = gCoreHighLoadHeap.PeekMinimum(index++);
-			} while (other != NULL && !core->CPUMask().Matches(mask));
+			} while (useMask && other != NULL && !other->CPUMask().Matches(mask));
 		}
 		coreLocker.Unlock();
 		ASSERT(other != NULL);
@@ -184,7 +179,7 @@ rebalance(const ThreadData* threadData)
 		return core;
 
 	CoreEntry* smallTaskCore = choose_small_task_core();
-	if (smallTaskCore == NULL || !smallTaskCore->CPUMask().Matches(mask))
+	if (smallTaskCore == NULL || (useMask && !smallTaskCore->CPUMask().Matches(mask)))
 		return core;
 	return smallTaskCore->GetLoad() + threadLoad < kHighLoad
 		? smallTaskCore : core;
diff --git a/src/system/kernel/scheduler/scheduler.cpp b/src/system/kernel/scheduler/scheduler.cpp
index 3ea4f8eb2d..aeaab25058 100644
--- a/src/system/kernel/scheduler/scheduler.cpp
+++ b/src/system/kernel/scheduler/scheduler.cpp
@@ -329,6 +329,9 @@ reschedule(int32 nextState)
 	Thread* oldThread = thread_get_current_thread();
 	ThreadData* oldThreadData = oldThread->scheduler_data;
 
+	CPUSet oldThreadMask;
+	bool useOldThreadMask, fetchedOldThreadMask = false;
+
 	oldThreadData->StopCPUTime();
 
 	SchedulerModeLocker modeLocker;
@@ -348,7 +351,11 @@ reschedule(int32 nextState)
 		case B_THREAD_READY:
 			enqueueOldThread = true;
 
-			if (!oldThreadData->IsIdle() && oldThreadData->GetCPUMask().GetBit(thisCPU)) {
+			oldThreadMask = oldThreadData->GetCPUMask();
+			useOldThreadMask = !oldThreadMask.IsEmpty();
+			fetchedOldThreadMask = true;
+
+			if (!oldThreadData->IsIdle() && (!useOldThreadMask || oldThreadMask.GetBit(thisCPU))) {
 				oldThreadData->Continues();
 				if (oldThreadData->HasQuantumEnded(oldThread->cpu->preempted,
 						oldThread->has_yielded)) {
@@ -394,15 +401,19 @@ reschedule(int32 nextState)
 		} else
 			nextThreadData = oldThreadData;
 	} else {
-		CPUSet mask = oldThreadData->GetCPUMask();
-		if (mask.IsEmpty())
-			mask.SetAll();
-		bool oldThreadShouldMigrate = !mask.GetBit(thisCPU);
+		if (!fetchedOldThreadMask) {
+			oldThreadMask = oldThreadData->GetCPUMask();
+			useOldThreadMask = !oldThreadMask.IsEmpty();
+			fetchedOldThreadMask = true;
+		}
+		bool oldThreadShouldMigrate = useOldThreadMask && !oldThreadMask.GetBit(thisCPU);
 		if (oldThreadShouldMigrate)
 			enqueueOldThread = false;
+
 		nextThreadData
 			= cpu->ChooseNextThread(enqueueOldThread ? oldThreadData : NULL,
 				putOldThreadAtBack);
+
 		if (oldThreadShouldMigrate) {
 			enqueue(oldThread, true);
 			// replace with the idle thread, if no other thread could be found
diff --git a/src/system/kernel/scheduler/scheduler_thread.cpp b/src/system/kernel/scheduler/scheduler_thread.cpp
index 75835de81b..1555e4eccf 100644
--- a/src/system/kernel/scheduler/scheduler_thread.cpp
+++ b/src/system/kernel/scheduler/scheduler_thread.cpp
@@ -60,12 +60,11 @@ ThreadData::_ChooseCPU(CoreEntry* core, bool& rescheduleNeeded) const
 	int32 threadPriority = GetEffectivePriority();
 
 	CPUSet mask = GetCPUMask();
-	if (mask.IsEmpty())
-		mask.SetAll();
-	ASSERT(mask.Matches(core->CPUMask()));
+	const bool useMask = !mask.IsEmpty();
+	ASSERT(!useMask || mask.Matches(core->CPUMask()));
 
 	if (fThread->previous_cpu != NULL && !fThread->previous_cpu->disabled
-		&& mask.GetBit(fThread->previous_cpu->cpu_num)) {
+			&& (!useMask || mask.GetBit(fThread->previous_cpu->cpu_num))) {
 		CPUEntry* previousCPU
 			= CPUEntry::GetCPU(fThread->previous_cpu->cpu_num);
 		if (previousCPU->Core() == core) {
@@ -83,7 +82,7 @@ ThreadData::_ChooseCPU(CoreEntry* core, bool& rescheduleNeeded) const
 	CPUEntry* cpu;
 	do {
 		cpu = core->CPUHeap()->PeekRoot(index++);
-	} while (cpu != NULL && !mask.GetBit(cpu->ID()));
+	} while (useMask && cpu != NULL && !mask.GetBit(cpu->ID()));
 	ASSERT(cpu != NULL);
 
 	if (CPUPriorityHeap::GetKey(cpu) < threadPriority) {
@@ -166,9 +165,12 @@ ThreadData::ChooseCoreAndCPU(CoreEntry*& targetCore, CPUEntry*& targetCPU)
 
 	bool rescheduleNeeded = false;
 
-	if (targetCore != NULL && !targetCore->CPUMask().Matches(GetCPUMask()))
+	CPUSet mask = GetCPUMask();
+	const bool useMask = !mask.IsEmpty();
+
+	if (targetCore != NULL && (useMask && !targetCore->CPUMask().Matches(mask)))
 		targetCore = NULL;
-	if (targetCPU != NULL && !GetCPUMask().GetBit(targetCPU->ID()))
+	if (targetCPU != NULL && (useMask && !mask.GetBit(targetCPU->ID())))
 		targetCPU = NULL;
 
 	if (targetCore == NULL && targetCPU != NULL)
@@ -177,10 +179,7 @@ ThreadData::ChooseCoreAndCPU(CoreEntry*& targetCore, CPUEntry*& targetCPU)
 		targetCPU = _ChooseCPU(targetCore, rescheduleNeeded);
 	else if (targetCore == NULL && targetCPU == NULL) {
 		targetCore = _ChooseCore();
-		CPUSet mask = GetCPUMask();
-		if (mask.IsEmpty())
-			mask.SetAll();
-		ASSERT(mask.Matches(targetCore->CPUMask()));
+		ASSERT(!useMask || mask.Matches(targetCore->CPUMask()));
 		targetCPU = _ChooseCPU(targetCore, rescheduleNeeded);
 	}
 
diff --git a/src/system/kernel/thread.cpp b/src/system/kernel/thread.cpp
index 9463afde11..6afd38926a 100644
--- a/src/system/kernel/thread.cpp
+++ b/src/system/kernel/thread.cpp
@@ -204,7 +204,6 @@ Thread::Thread(const char* name, thread_id threadID, struct cpu_ent* cpu)
 {
 	id = threadID >= 0 ? threadID : allocate_thread_id();
 	visible = false;
-	cpumask.SetAll();
 
 	// init locks
 	char lockName[32];
@@ -2755,7 +2754,6 @@ thread_init(kernel_args *args)
 		thread->team = team_get_kernel_team();
 		thread->priority = B_IDLE_PRIORITY;
 		thread->state = B_THREAD_RUNNING;
-		thread->cpumask.SetAll();
 
 		sprintf(name, "idle thread %" B_PRIu32 " kstack", i + 1);
 		thread->kernel_stack_area = find_area(name);