hw: optimize ipc capability allocation

In preparation of ipc receive, by now a bunch of capabilities got
allocated to be ready iin case of capability receiption. After that
unuse slots were freed again. This overhead of senseless (de-)allocations
is replaced in this commit by just restock capability slots that got
used by the last receive.

Fix #3640

repos/base-hw/src/core/kernel/thread.cc

@@ -35,19 +35,34 @@ extern "C" void _core_start(void);
 
 using namespace Kernel;
 
-static inline void free_obj_id_ref(Pd &pd, void *ptr)
+
+void Thread::_ipc_alloc_recv_caps(unsigned cap_count)
 {
-	pd.platform_pd().capability_slab().free(ptr, sizeof(Object_identity_reference));
+	Genode::Allocator &slab = pd().platform_pd().capability_slab();
+	for (unsigned i = 0; i < cap_count; i++) {
+		if (_obj_id_ref_ptr[i] == nullptr)
+			_obj_id_ref_ptr[i] = slab.alloc(sizeof(Object_identity_reference));
+	}
+	_ipc_rcv_caps = cap_count;
+}
+
+
+void Thread::_ipc_free_recv_caps()
+{
+	for (unsigned i = 0; i < _ipc_rcv_caps; i++) {
+		if (_obj_id_ref_ptr[i]) {
+			Genode::Allocator &slab = pd().platform_pd().capability_slab();
+			slab.free(_obj_id_ref_ptr[i], sizeof(Object_identity_reference));
+		}
+	}
+	_ipc_rcv_caps = 0;
 }
 
 
 void Thread::_ipc_init(Genode::Native_utcb &utcb, Thread &starter)
 {
 	_utcb = &utcb;
-	_ipc_rcv_caps = starter._utcb->cap_cnt();
-	Genode::Allocator &slab = pd().platform_pd().capability_slab();
-	for (unsigned i = 0; i < _ipc_rcv_caps; i++)
-		_obj_id_ref_ptr[i] = slab.alloc(sizeof(Object_identity_reference));
+	_ipc_alloc_recv_caps(starter._utcb->cap_cnt());
 	ipc_copy_msg(starter);
 }
 
@@ -66,20 +81,16 @@ void Thread::ipc_copy_msg(Thread &sender)
 
 		capid_t id = sender._utcb->cap_get(i);
 
-		/* if there is no capability to send, just free the pre-allocation */
-		if (i >= sender._utcb->cap_cnt()) {
-			free_obj_id_ref(pd(), _obj_id_ref_ptr[i]);
-			continue;
-		}
+		/* if there is no capability to send, nothing to do */
+		if (i >= sender._utcb->cap_cnt()) { continue; }
 
 		/* lookup the capability id within the caller's cap space */
 		Reference *oir = (id == cap_id_invalid())
 			? nullptr : sender.pd().cap_tree().find(id);
 
-		/* if the caller's capability is invalid, free the pre-allocation */
+		/* if the caller's capability is invalid, continue */
 		if (!oir) {
 			_utcb->cap_add(cap_id_invalid());
-			free_obj_id_ref(pd(), _obj_id_ref_ptr[i]);
 			continue;
 		}
 
@@ -89,10 +100,8 @@ void Thread::ipc_copy_msg(Thread &sender)
 		/* if it is not found, and the target is not core, create a reference */
 		if (!dst_oir && (&pd() != &core_pd())) {
 			dst_oir = oir->factory(_obj_id_ref_ptr[i], pd());
-			if (!dst_oir)
-				free_obj_id_ref(pd(), _obj_id_ref_ptr[i]);
-		} else /* otherwise free the pre-allocation */
-			free_obj_id_ref(pd(), _obj_id_ref_ptr[i]);
+			if (dst_oir) _obj_id_ref_ptr[i] = nullptr;
+		}
 
 		if (dst_oir) dst_oir->add_to_utcb();
 
@@ -405,12 +414,7 @@ void Thread::_call_delete_thread()
 void Thread::_call_await_request_msg()
 {
 	if (_ipc_node.can_await_request()) {
-		unsigned const rcv_caps = user_arg_1();
-		Genode::Allocator &slab = pd().platform_pd().capability_slab();
-		for (unsigned i = 0; i < rcv_caps; i++)
-			_obj_id_ref_ptr[i] = slab.alloc(sizeof(Object_identity_reference));
-
-		_ipc_rcv_caps = rcv_caps;
+		_ipc_alloc_recv_caps(user_arg_1());
 		_ipc_node.await_request();
 		if (_ipc_node.awaits_request()) {
 			_become_inactive(AWAITS_IPC);
@@ -473,13 +477,8 @@ void Thread::_call_send_request_msg()
 	if (!_ipc_node.can_send_request()) {
 		Genode::raw("IPC send request: bad state");
 	} else {
-		unsigned const rcv_caps = user_arg_2();
-		Genode::Allocator &slab = pd().platform_pd().capability_slab();
-		for (unsigned i = 0; i < rcv_caps; i++)
-			_obj_id_ref_ptr[i] = slab.alloc(sizeof(Object_identity_reference));
-
+		_ipc_alloc_recv_caps(user_arg_2());
 		_ipc_capid    = oir ? oir->capid() : cap_id_invalid();
-		_ipc_rcv_caps = rcv_caps;
 		_ipc_node.send_request(dst->_ipc_node, help);
 	}
 
@@ -832,6 +831,9 @@ Thread::Thread(unsigned const priority, unsigned const quota,
 	_label(label), _core(core), regs(core) { }
 
 
+Thread::~Thread() { _ipc_free_recv_caps(); }
+
+
 void Thread::print(Genode::Output &out) const
 {
 	Genode::print(out, _pd ? _pd->platform_pd().label() : "?");

repos/base-hw/src/core/kernel/thread.h

@@ -125,7 +125,9 @@ class Kernel::Thread : private Kernel::Object, public Cpu_job, private Timeout
 			DEAD                        = 7,
 		};
 
-		void                  *_obj_id_ref_ptr[Genode::Msgbuf_base::MAX_CAPS_PER_MSG];
+		enum { MAX_RCV_CAPS = Genode::Msgbuf_base::MAX_CAPS_PER_MSG };
+
+		void                  *_obj_id_ref_ptr[MAX_RCV_CAPS] { nullptr };
 		Ipc_node               _ipc_node;
 		capid_t                _ipc_capid                { cap_id_invalid() };
 		size_t                 _ipc_rcv_caps             { 0 };
@@ -269,6 +271,8 @@ class Kernel::Thread : private Kernel::Object, public Cpu_job, private Timeout
 			kobj.destruct();
 		}
 
+		void _ipc_alloc_recv_caps(unsigned rcv_cap_count);
+		void _ipc_free_recv_caps();
 		void _ipc_init(Genode::Native_utcb &utcb, Thread &callee);
 
 	public:
@@ -294,6 +298,8 @@ class Kernel::Thread : private Kernel::Object, public Cpu_job, private Timeout
 		Thread(char const * const label)
 		: Thread(Cpu_priority::MIN, 0, label, true) { }
 
+		~Thread();
+
 
 		/**************************
 		 ** Support for syscalls **

repos/base-hw/src/core/platform_pd.cc

@@ -132,10 +132,6 @@ bool Platform_pd::bind_thread(Platform_thread &t)
 }
 
 
-void Platform_pd::unbind_thread(Platform_thread &t) {
-	t.join_pd(nullptr, false, Address_space::weak_ptr()); }
-
-
 void Platform_pd::assign_parent(Native_capability parent)
 {
 	if (!_parent.valid() && parent.valid())

repos/base-hw/src/core/platform_pd.h

@@ -209,11 +209,6 @@ class Genode::Platform_pd : public  Hw::Address_space,
 		 */
 		bool bind_thread(Platform_thread &);
 
-		/**
-		 * Unbind thread from protection domain
-		 */
-		void unbind_thread(Platform_thread &);
-
 		/**
 		 * Assign parent interface to protection domain
 		 */