f1u,cu_up: run dl_notif_timer only when needed

Author: robertfalkenberg

lib/f1u/cu_up/f1u_bearer_impl.cpp

@@ -32,7 +32,6 @@ f1u_bearer_impl::f1u_bearer_impl(uint32_t                  ue_index,
 {
   dl_notif_timer.set(std::chrono::milliseconds(f1u_dl_notif_time_ms),
                      [this](timer_id_t tid) { on_expired_dl_notif_timer(); });
-  dl_notif_timer.run();
 }
 
 void f1u_bearer_impl::handle_pdu(nru_ul_message msg)
@@ -85,11 +84,18 @@ void f1u_bearer_impl::handle_sdu(pdcp_tx_pdu sdu)
   // attach discard blocks (if any)
   fill_discard_blocks(msg);
 
+  // stop backoff timer
+  dl_notif_timer.stop();
+
   tx_pdu_notifier.on_new_pdu(std::move(msg));
 }
 
 void f1u_bearer_impl::discard_sdu(uint32_t pdcp_sn)
 {
+  // start backoff timer
+  if (!dl_notif_timer.is_running()) {
+    dl_notif_timer.run();
+  }
   if (discard_blocks.empty()) {
     discard_blocks.push_back(nru_pdcp_sn_discard_block{});
     nru_pdcp_sn_discard_block& block = discard_blocks.back();
@@ -124,8 +130,6 @@ void f1u_bearer_impl::fill_discard_blocks(nru_dl_message& msg)
     msg.dl_user_data.discard_blocks = std::move(discard_blocks);
     discard_blocks                  = {};
   }
-  // restart UL notification timer
-  dl_notif_timer.run();
 }
 
 void f1u_bearer_impl::on_expired_dl_notif_timer()
@@ -137,7 +141,13 @@ void f1u_bearer_impl::on_expired_dl_notif_timer()
 void f1u_bearer_impl::flush_discard_blocks()
 {
   nru_dl_message msg = {};
+
+  // attach discard blocks (if any)
   fill_discard_blocks(msg);
+
+  // stop backoff timer
+  dl_notif_timer.stop();
+
   if (msg.dl_user_data.discard_blocks.has_value()) {
     logger.log_debug("Sending discard blocks");
     tx_pdu_notifier.on_new_pdu(std::move(msg));

tests/unittests/f1u/cu_up/f1u_cu_up_bearer_test.cpp

@@ -125,6 +125,9 @@ TEST_F(f1u_cu_up_test, tx_discard)
   constexpr uint32_t pdu_size = 10;
   constexpr uint32_t pdcp_sn  = 123;
 
+  // advance time by one to ensure timer is stopped and ignores this tick
+  tick();
+
   f1u->discard_sdu(pdcp_sn);
   // advance time just before the timer-based DL notification is triggered
   for (uint32_t t = 0; t < f1u_dl_notif_time_ms - 1; t++) {
@@ -161,6 +164,9 @@ TEST_F(f1u_cu_up_test, tx_discard)
   tester->tx_msg_list.pop_front();
   ASSERT_TRUE(tester->tx_msg_list.empty());
 
+  // advance time by one to ensure timer is stopped and ignores this tick
+  tick();
+
   f1u->discard_sdu(pdcp_sn + 7);
   // advance time just before the timer-based DL notification is triggered
   for (uint32_t t = 0; t < f1u_dl_notif_time_ms - 1; t++) {