diff --git a/src/ifcconvert/IfcConvert.cpp b/src/ifcconvert/IfcConvert.cpp
index 910d17ad18..8847d803e2 100644
--- a/src/ifcconvert/IfcConvert.cpp
+++ b/src/ifcconvert/IfcConvert.cpp
@@ -122,6 +122,7 @@ bool rename_file(const std::string& old_filename, const std::string& new_filenam
 static std::stringstream log_stream;
 void write_log(bool);
 void fix_quantities(IfcParse::IfcFile&, bool, bool, bool);
+std::string format_duration(time_t start, time_t end);
 
 /// @todo make the filters non-global
 IfcGeom::entity_filter entity_filter; // Entity filter is used always by default.
@@ -475,10 +476,14 @@ int main(int argc, char** argv)
 		int exit_code = EXIT_FAILURE;
 		try {
 			if (init_input_file(input_filename, ifc_file, no_progress || quiet, mmap)) {
+				time_t start, end;
+				time(&start);
 				XmlSerializer s(ifc_file, output_temp_filename);
 				Logger::Status("Writing XML output...");
 				s.finalize();
-				Logger::Status("Done!");
+				time(&end);
+				Logger::Status("Done! Conversion took " +  format_duration(start, end));
+
 				rename_file(output_temp_filename, output_filename);
 				exit_code = EXIT_SUCCESS;
 			}
@@ -786,28 +791,33 @@ int main(int argc, char** argv)
 
 	time(&end);
 
-	if (!quiet) {
-		int seconds = (int)difftime(end, start);
-		std::stringstream msg;
-		int minutes = seconds / 60;
-		seconds = seconds % 60;
-		msg << "\nConversion took";
-		if (minutes > 0) {
-			msg << " " << minutes << " minute";
-			if (minutes > 1) {
-				msg << "s";
-			}
-		}
-		msg << " " << seconds << " second";
-		if (seconds > 1) {
-			msg << "s";
-		}
-		Logger::Status(msg.str());
-	}
+    if (!quiet) {
+        Logger::Status("\nConversion took " +  format_duration(start, end));
+    }
 
     return successful ? EXIT_SUCCESS : EXIT_FAILURE;
 }
 
+std::string format_duration(time_t start, time_t end)
+{
+    int seconds = (int)difftime(end, start);
+    std::stringstream ss;
+    int minutes = seconds / 60;
+    seconds = seconds % 60;
+    if (minutes > 0) {
+        ss << minutes << " minute";
+        if (minutes == 0 || minutes > 1) {
+            ss << "s";
+        }
+        ss << " ";
+    }
+    ss << seconds << " second";
+    if (seconds == 0 || seconds > 1) {
+        ss << "s";
+    }
+    return ss.str();
+}
+
 void write_log(bool header) {
 	std::string log = log_stream.str();
 	if (!log.empty()) {
@@ -821,10 +831,12 @@ void write_log(bool header) {
 #include <boost/algorithm/string/predicate.hpp>
 
 bool init_input_file(const std::string& filename, IfcParse::IfcFile*& ifc_file, bool no_progress, bool mmap) {
+    time_t start, end;
 
     // Prevent IfcFile::Init() prints by setting output to null temporarily
     if (no_progress) { Logger::SetOutput(NULL, &log_stream); }
 
+    time(&start);
 #ifdef USE_MMAP
 	ifc_file = new IfcParse::IfcFile(filename, mmap);
 #else
@@ -841,8 +853,10 @@ bool init_input_file(const std::string& filename, IfcParse::IfcFile*& ifc_file,
         Logger::Error("Unable to parse input file '" + filename + "'");
         return false;
     }
+    time(&end);
 
     if (no_progress) { Logger::SetOutput(&std::cout, &log_stream); }
+    else {  Logger::Status("Parsing input file took " + format_duration(start, end)); }
 
     return true;
 
diff --git a/src/ifcgeom_schema_agnostic/Kernel.cpp b/src/ifcgeom_schema_agnostic/Kernel.cpp
index ecd738a048..e6def6a42a 100644
--- a/src/ifcgeom_schema_agnostic/Kernel.cpp
+++ b/src/ifcgeom_schema_agnostic/Kernel.cpp
@@ -151,15 +151,6 @@ IfcUtil::IfcBaseEntity* IfcGeom::Kernel::get_decomposing_entity(IfcUtil::IfcBase
 }
 
 namespace {
-
-        // LayerAssignments renamed from plural to singular, LayerAssignment, so work around that
-        IfcEntityList::ptr getLayerAssignments(Ifc2x3::IfcRepresentationItem* item) {
-                return item->LayerAssignments()->generalize();
-        }
-        IfcEntityList::ptr getLayerAssignments(Ifc4::IfcRepresentationItem* item) {
-                return item->LayerAssignment()->generalize();
-        }
-
 	template <typename Schema>
 	static std::map<std::string, IfcUtil::IfcBaseEntity*> get_layers_impl(typename Schema::IfcProduct* prod) {
 		std::map<std::string, IfcUtil::IfcBaseEntity*> layers;
@@ -172,14 +163,6 @@ namespace {
 					layers[(*jt)->Name()] = *jt;
 				}
 			}
-
-			typename Schema::IfcRepresentationItem::list::ptr items = r->as<typename Schema::IfcRepresentationItem>();
-			for (typename Schema::IfcRepresentationItem::list::it it = items->begin(); it != items->end(); ++it) {
-				typename Schema::IfcPresentationLayerAssignment::list::ptr a = getLayerAssignments(*it)->template as<typename Schema::IfcPresentationLayerAssignment>();
-				for (typename Schema::IfcPresentationLayerAssignment::list::it jt = a->begin(); jt != a->end(); ++jt) {
-					layers[(*jt)->Name()] = *jt;
-				}
-			}
 		}
 		return layers;
 	}
diff --git a/src/ifcparse/IfcEntityList.h b/src/ifcparse/IfcEntityList.h
index 263ab2cf6b..784f90a63f 100644
--- a/src/ifcparse/IfcEntityList.h
+++ b/src/ifcparse/IfcEntityList.h
@@ -40,6 +40,7 @@ public:
 	it end();
 	IfcUtil::IfcBaseClass* operator[] (int i);
 	unsigned int size() const;
+    void reserve(unsigned capacity);
 	bool contains(IfcUtil::IfcBaseClass*) const;
 	template <class U>
 	typename U::list::ptr as() {
diff --git a/src/ifcparse/IfcFile.h b/src/ifcparse/IfcFile.h
index a3120ec620..f613c938c9 100644
--- a/src/ifcparse/IfcFile.h
+++ b/src/ifcparse/IfcFile.h
@@ -41,6 +41,7 @@ public:
 	typedef boost::unordered_map<unsigned int, IfcUtil::IfcBaseClass*> entity_by_id_t;
 	typedef std::map<std::string, IfcUtil::IfcBaseClass*> entity_by_guid_t;
 	typedef std::map<unsigned int, std::vector<unsigned int> > entities_by_ref_t;
+	typedef std::map<unsigned int, IfcEntityList::ptr> ref_map_t;
 	typedef entity_by_id_t::const_iterator const_iterator;
 
 	class type_iterator : private entities_by_type_t::const_iterator {
@@ -86,6 +87,7 @@ private:
 	entities_by_type_t bytype;
 	entities_by_type_t bytype_excl;
 	entities_by_ref_t byref;
+	ref_map_t by_ref_cached_;
 	entity_by_guid_t byguid;
 	entity_entity_map_t entity_file_map;
 
@@ -181,6 +183,10 @@ public:
 
 	IfcEntityList::ptr getInverse(int instance_id, const IfcParse::declaration* type, int attribute_index);
 
+	/// Marks entity as modified so that potential cache for it is invalidated.
+	/// @todo Currently the whole cache is invalidated. Implement more fine-grained invalidation.
+	void mark_entity_as_modified(int id);
+
 	unsigned int FreshId() { return ++MaxId; }
 
 	IfcUtil::IfcBaseClass* addEntity(IfcUtil::IfcBaseClass* entity);
diff --git a/src/ifcparse/IfcParse.cpp b/src/ifcparse/IfcParse.cpp
index 78fa39f312..99ebefe959 100644
--- a/src/ifcparse/IfcParse.cpp
+++ b/src/ifcparse/IfcParse.cpp
@@ -1257,7 +1257,9 @@ void IfcEntityInstanceData::setArgument(unsigned int i, Argument* a, IfcUtil::Ar
 	if (this->file) {
 		register_inverse_visitor visitor(*this->file, *this);
 		apply_individual_instance_visitor(copy).apply(visitor);
-	}	
+
+		this->file->mark_entity_as_modified(id_);
+	}
 
 	attributes_[i] = copy;
 }
@@ -1504,6 +1506,11 @@ IfcEntityList::ptr IfcFile::traverse(IfcUtil::IfcBaseClass* instance, int max_le
 	return IfcParse::traverse(instance, max_level);
 }
 
+void IfcFile::mark_entity_as_modified(int /*id*/)
+{
+	by_ref_cached_.clear();
+}
+
 void IfcFile::addEntities(IfcEntityList::ptr es) {
 	for( IfcEntityList::it i = es->begin(); i != es->end(); ++ i ) {
 		addEntity(*i);
@@ -1868,17 +1875,25 @@ IfcEntityList::ptr IfcFile::instances_by_type(const std::string& t) {
 
 IfcEntityList::ptr IfcFile::instances_by_reference(int t) {
 	entities_by_ref_t::const_iterator it = byref.find(t);
-	IfcEntityList::ptr return_value;
+	IfcEntityList::ptr ret;
 	if (it != byref.end()) {
-		const std::vector<unsigned>& ids = it->second;
-		for (std::vector<unsigned>::const_iterator jt = ids.begin(); jt != ids.end(); ++jt) {
-			if (!return_value) {
-				return_value.reset(new IfcEntityList);
-			}
-			return_value->push(instance_by_id(*jt));
-		}
+        ref_map_t::const_iterator cached_it = by_ref_cached_.find(t);
+        if (cached_it != by_ref_cached_.end()) {
+            ret = cached_it->second;
+        }
+        else {
+            if (it->second.size()) {
+                ret.reset(new IfcEntityList);            
+                ret->reserve((unsigned)it->second.size());
+                const std::vector<unsigned>& ids = it->second;
+                for (std::vector<unsigned>::const_iterator jt = ids.begin(); jt != ids.end(); ++jt) {
+                    ret->push(instance_by_id(*jt));
+                }
+            }
+            by_ref_cached_[t] = ret;
+        }
 	}
-	return return_value;
+	return ret;
 }
 
 IfcUtil::IfcBaseClass* IfcFile::instance_by_id(int id) {
diff --git a/src/ifcparse/IfcUtil.cpp b/src/ifcparse/IfcUtil.cpp
index 48ea296329..0aecf0757f 100644
--- a/src/ifcparse/IfcUtil.cpp
+++ b/src/ifcparse/IfcUtil.cpp
@@ -42,6 +42,7 @@ void IfcEntityList::push(const IfcEntityList::ptr& l) {
 	}
 }
 unsigned int IfcEntityList::size() const { return (unsigned int) ls.size(); }
+void IfcEntityList::reserve(unsigned capacity) { ls.reserve((size_t)capacity); }
 IfcEntityList::it IfcEntityList::begin() { return ls.begin(); }
 IfcEntityList::it IfcEntityList::end() { return ls.end(); }
 IfcUtil::IfcBaseClass* IfcEntityList::operator[] (int i) {