Drop traffic in PDCP if RLC buffer is full

If the buffer in the RLC is full, testing the buffer state over and over again
slows the DL traffic down. In order to circumvent this, the PDCP will drop any
data during a configurable time (compile-time) before it delivers data to RLC
again.

To change this, see the constant TM_SKIP_FULL_BUF_MS in pdcp.h.

openair2/LAYER2/PDCP_v10.1.0/pdcp.c

@@ -169,6 +169,11 @@ boolean_t pdcp_data_req(
     start_meas(&UE_pdcp_stats[ctxt_pP->module_id].data_req);
   }
 
+  for (pdcp_uid = 0; pdcp_uid < MAX_MOBILES_PER_ENB; ++pdcp_uid) {
+    if (pdcp_enb[ctxt_pP->module_id].rnti[pdcp_uid] == ctxt_pP->rnti)
+      break;
+  }
+
   // PDCP transparent mode for MBMS traffic
 
   if (modeP == PDCP_TRANSMISSION_MODE_TRANSPARENT) {
@@ -366,13 +371,24 @@ boolean_t pdcp_data_req(
     LOG_DUMPMSG(PDCP,DEBUG_PDCP,(char *)pdcp_pdu_p->data,pdcp_pdu_size,
                 "[MSG] PDCP DL %s PDU on rb_id %d\n",(srb_flagP)? "CONTROL" : "DATA", rb_idP);
 
-    rlc_status = rlc_data_req(ctxt_pP, srb_flagP, MBMS_FLAG_NO, rb_idP, muiP, confirmP, pdcp_pdu_size, pdcp_pdu_p
+    /* if RLC buffer for this UE has been full, we want to skip all subsequent
+     * traffic for TM_SKIP_FULL_BUF_MS ms. Afterwards, it will be checkd again */
+    if (pdcp_enb[ctxt_pP->module_id].time_buf_full[pdcp_uid] == 0
+        || pdcp_enb[ctxt_pP->module_id].sfn - pdcp_enb[ctxt_pP->module_id].time_buf_full[pdcp_uid] >= TM_SKIP_FULL_BUF_MS) {
+      pdcp_enb[ctxt_pP->module_id].time_buf_full[pdcp_uid] = 0;
+      rlc_status = rlc_data_req(ctxt_pP, srb_flagP, MBMS_FLAG_NO, rb_idP, muiP,
+                                confirmP, pdcp_pdu_size, pdcp_pdu_p
 #if (RRC_VERSION >= MAKE_VERSION(14, 0, 0))
                                 ,sourceL2Id
                                 ,destinationL2Id
 #endif
                                );
-
+    } else {
+      /* RLC would free pdcp_pdu_p, but since we skip it, have to do it
+       * ourselves and fake normal operation */
+      free_mem_block(pdcp_pdu_p, __func__);
+      rlc_status = RLC_OP_SKIPPED_FUL_BUF;
+    }
   }
 
   switch (rlc_status) {
@@ -392,10 +408,19 @@ boolean_t pdcp_data_req(
     break;
 
   case RLC_OP_STATUS_OUT_OF_RESSOURCES:
+    pdcp_enb[ctxt_pP->module_id].time_buf_full[pdcp_uid] = pdcp_enb[ctxt_pP->module_id].sfn;
     LOG_W(PDCP, "Data sending request over RLC failed with 'Out of Resources' reason!\n");
+    int h = TM_SKIP_FULL_BUF_MS;
+    LOG_W(PDCP, "Blocking incoming traffic for %d ms\n", h);
     ret= FALSE;
     break;
 
+  case RLC_OP_SKIPPED_FUL_BUF:
+    LOG_D(PDCP, "Skipping RLC request due to full buffer\n");
+    /* fake good return so that GTP doesn't spam us */
+    ret = TRUE;
+    break;
+
   default:
     LOG_W(PDCP, "RLC returned an unknown status code after PDCP placed the order to send some data (Status Code:%d)\n", rlc_status);
     ret= FALSE;
@@ -408,16 +433,6 @@ boolean_t pdcp_data_req(
     stop_meas(&UE_pdcp_stats[ctxt_pP->module_id].data_req);
   }
 
-  /*
-   * Control arrives here only if rlc_data_req() returns RLC_OP_STATUS_OK
-   * so we return TRUE afterwards
-   */
-  
-  for (pdcp_uid=0; pdcp_uid< MAX_MOBILES_PER_ENB;pdcp_uid++){
-    if (pdcp_enb[ctxt_pP->module_id].rnti[pdcp_uid] == ctxt_pP->rnti ) 
-      break;
-  }
-
   //LOG_I(PDCP,"ueid %d lcid %d tx seq num %d\n", pdcp_uid, rb_idP+rb_offset, current_sn);
   Pdcp_stats_tx[ctxt_pP->module_id][pdcp_uid][rb_idP+rb_offset]++;
   Pdcp_stats_tx_tmp_w[ctxt_pP->module_id][pdcp_uid][rb_idP+rb_offset]++;
@@ -1066,6 +1081,7 @@ void pdcp_add_UE(const protocol_ctxt_t* const  ctxt_pP){
       if (pdcp_enb[ctxt_pP->module_id].rnti[i] == 0 ){
 	pdcp_enb[ctxt_pP->module_id].rnti[i]=ctxt_pP->rnti;
 	pdcp_enb[ctxt_pP->module_id].uid[i]=i;
+        pdcp_enb[ctxt_pP->module_id].time_buf_full[i] = 0;
 	pdcp_enb[ctxt_pP->module_id].num_ues++;
 	printf("add new uid is %d %x\n\n", i, ctxt_pP->rnti);
 	// ret=1;

openair2/LAYER2/PDCP_v10.1.0/pdcp.h

@@ -106,6 +106,8 @@ typedef struct pdcp_enb_s {
   uint16_t uid[MAX_MOBILES_PER_ENB];
   rnti_t rnti[MAX_MOBILES_PER_ENB];
   uint16_t num_ues;
+#define TM_SKIP_FULL_BUF_MS (500)
+  uint64_t time_buf_full[MAX_MOBILES_PER_ENB];
   
   uint64_t sfn;
   frame_t  frame;

openair2/LAYER2/RLC/rlc.h

@@ -67,6 +67,7 @@ typedef uint64_t hash_key_t;
 #define  RLC_OP_STATUS_BAD_PARAMETER     22
 #define  RLC_OP_STATUS_INTERNAL_ERROR    2
 #define  RLC_OP_STATUS_OUT_OF_RESSOURCES 3
+#define  RLC_OP_SKIPPED_FUL_BUF          4
 
 #define  RLC_MUI_UNDEFINED     (mui_t)0