Index: libcfa/src/concurrency/kernel.cfa
===================================================================
--- libcfa/src/concurrency/kernel.cfa	(revision 3df86ccdb84e0936b9d0bb87c4e1d4c237999422)
+++ libcfa/src/concurrency/kernel.cfa	(revision 34b8cb78d5c3fe9fee27074af9317f20dd531a38)
@@ -126,5 +126,4 @@
 static void mark_idle (__cluster_proc_list & idles, processor & proc);
 static void mark_awake(__cluster_proc_list & idles, processor & proc);
-static [unsigned idle, unsigned total, * processor] query_idles( & __cluster_proc_list idles );
 
 extern void __cfa_io_start( processor * );
@@ -766,16 +765,13 @@
 
 	// Check if there is a sleeping processor
-	processor * p;
-	unsigned idle;
-	unsigned total;
-	[idle, total, p] = query_idles(this->procs);
+	int fd = __atomic_load_n(&this->procs.fd, __ATOMIC_SEQ_CST);
 
 	// If no one is sleeping, we are done
-	if( idle == 0 ) return;
+	if( fd == 0 ) return;
 
 	// We found a processor, wake it up
 	eventfd_t val;
 	val = 1;
-	eventfd_write( p->idle, val );
+	eventfd_write( fd, val );
 
 	#if !defined(__CFA_NO_STATISTICS__)
@@ -813,4 +809,6 @@
 		remove(proc);
 		insert_first(this.idles, proc);
+
+		__atomic_store_n(&this.fd, proc.idle, __ATOMIC_SEQ_CST);
 	unlock( this );
 	/* paranoid */ verify( ! __preemption_enabled() );
@@ -824,25 +822,7 @@
 		remove(proc);
 		insert_last(this.actives, proc);
+
+		__atomic_store_n(&this.fd, this.idles`first.idle, __ATOMIC_SEQ_CST);
 	unlock( this );
-	/* paranoid */ verify( ! __preemption_enabled() );
-}
-
-static [unsigned idle, unsigned total, * processor] query_idles( & __cluster_proc_list this ) {
-	/* paranoid */ verify( ! __preemption_enabled() );
-	/* paranoid */ verify( ready_schedule_islocked() );
-
-	for() {
-		uint64_t l = __atomic_load_n(&this.lock, __ATOMIC_SEQ_CST);
-		if( 1 == (l % 2) ) { Pause(); continue; }
-		unsigned idle    = this.idle;
-		unsigned total   = this.total;
-		processor * proc = &this.idles`first;
-		// Compiler fence is unnecessary, but gcc-8 and older incorrectly reorder code without it
-		asm volatile("": : :"memory");
-		if(l != __atomic_load_n(&this.lock, __ATOMIC_SEQ_CST)) { Pause(); continue; }
-		return [idle, total, proc];
-	}
-
-	/* paranoid */ verify( ready_schedule_islocked() );
 	/* paranoid */ verify( ! __preemption_enabled() );
 }
@@ -906,10 +886,10 @@
 		if(head == tail) return false;
 		#if OLD_MAIN
-		ready_schedule_lock();
-		ret = __cfa_io_drain( proc );
-		ready_schedule_unlock();
+			ready_schedule_lock();
+			ret = __cfa_io_drain( proc );
+			ready_schedule_unlock();
 		#else
 			ret = __cfa_io_drain( proc );
-	#endif
+		#endif
 	#endif
 	return ret;
Index: libcfa/src/concurrency/kernel.hfa
===================================================================
--- libcfa/src/concurrency/kernel.hfa	(revision 3df86ccdb84e0936b9d0bb87c4e1d4c237999422)
+++ libcfa/src/concurrency/kernel.hfa	(revision 34b8cb78d5c3fe9fee27074af9317f20dd531a38)
@@ -195,5 +195,8 @@
 struct __cluster_proc_list {
 	// Spin lock protecting the queue
-	volatile uint64_t lock;
+	__spinlock_t lock;
+
+	// FD to use to wake a processor
+	volatile int fd;
 
 	// Total number of processors
Index: libcfa/src/concurrency/kernel/startup.cfa
===================================================================
--- libcfa/src/concurrency/kernel/startup.cfa	(revision 3df86ccdb84e0936b9d0bb87c4e1d4c237999422)
+++ libcfa/src/concurrency/kernel/startup.cfa	(revision 34b8cb78d5c3fe9fee27074af9317f20dd531a38)
@@ -584,5 +584,5 @@
 // Cluster
 static void ?{}(__cluster_proc_list & this) {
-	this.lock  = 0;
+	this.fd    = 0;
 	this.idle  = 0;
 	this.total = 0;