tcp: retry lost retransmits

Add heuristic that detects lost retransmitted segments and retries
sending them.

Type: feature

Change-Id: I34d1bb16799e1993779222eb2bfad4b40704159e
Signed-off-by: Florin Coras <fcoras@cisco.com>

1 files changed, 118 insertions, 132 deletions

diff --git a/src/vnet/tcp/tcp_input.c b/src/vnet/tcp/tcp_input.c
index b49b8e8fd77..f177f5f4753 100755
--- a/src/vnet/tcp/tcp_input.c
+++ b/src/vnet/tcp/tcp_input.c
@@ -629,34 +629,6 @@ tcp_program_dequeue (tcp_worker_ctx_t * wrk, tcp_connection_t * tc)
   tc->burst_acked += tc->bytes_acked;
 }
 
-/**
- * Check if duplicate ack as per RFC5681 Sec. 2
- */
-static u8
-tcp_ack_is_dupack (tcp_connection_t * tc, vlib_buffer_t * b, u32 prev_snd_wnd,
-		   u32 prev_snd_una)
-{
-  return ((vnet_buffer (b)->tcp.ack_number == prev_snd_una)
-	  && seq_gt (tc->snd_nxt, tc->snd_una)
-	  && (vnet_buffer (b)->tcp.seq_end == vnet_buffer (b)->tcp.seq_number)
-	  && (prev_snd_wnd == tc->snd_wnd));
-}
-
-/**
- * Checks if ack is a congestion control event.
- */
-static u8
-tcp_ack_is_cc_event (tcp_connection_t * tc, vlib_buffer_t * b,
-		     u32 prev_snd_wnd, u32 prev_snd_una, u8 * is_dack)
-{
-  /* Check if ack is duplicate. Per RFC 6675, ACKs that SACK new data are
-   * defined to be 'duplicate' */
-  *is_dack = tc->sack_sb.last_sacked_bytes
-    || tcp_ack_is_dupack (tc, b, prev_snd_wnd, prev_snd_una);
-
-  return ((*is_dack || tcp_in_cong_recovery (tc)) && !tcp_is_lost_fin (tc));
-}
-
 #ifndef CLIB_MARCH_VARIANT
 static u32
 scoreboard_hole_index (sack_scoreboard_t * sb, sack_scoreboard_hole_t * hole)
@@ -920,7 +892,7 @@ scoreboard_next_rxt_hole (sack_scoreboard_t * sb,
 }
 
 void
-scoreboard_init_high_rxt (sack_scoreboard_t * sb, u32 snd_una)
+scoreboard_init_rxt (sack_scoreboard_t * sb, u32 snd_una)
 {
   sack_scoreboard_hole_t *hole;
   hole = scoreboard_first_hole (sb);
@@ -975,7 +947,7 @@ scoreboard_clear_reneging (sack_scoreboard_t * sb, u32 start, u32 end)
   last_hole->is_lost = 1;
   sb->tail = scoreboard_hole_index (sb, last_hole);
   sb->high_sacked = start;
-  scoreboard_init_high_rxt (sb, start);
+  scoreboard_init_rxt (sb, start);
 }
 
 #endif /* CLIB_MARCH_VARIANT */
@@ -1203,6 +1175,8 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
   ASSERT (sb->last_lost_bytes <= sb->lost_bytes);
   ASSERT ((ack - tc->snd_una) + sb->last_sacked_bytes
 	  - sb->last_bytes_delivered >= sb->rxt_sacked);
+  ASSERT ((ack - tc->snd_una) >= tc->sack_sb.last_bytes_delivered
+	  || (tc->flags & TCP_CONN_FINSNT));
 
   TCP_EVT (TCP_EVT_CC_SCOREBOARD, tc);
 }
@@ -1261,9 +1235,11 @@ tcp_cc_init_congestion (tcp_connection_t * tc)
   tc->snd_rxt_bytes = 0;
   tc->rxt_delivered = 0;
   tc->prr_delivered = 0;
+  tc->prr_start = tc->snd_una;
   tc->prev_ssthresh = tc->ssthresh;
   tc->prev_cwnd = tc->cwnd;
 
+  tc->snd_rxt_ts = tcp_tstamp (tc);
   tcp_cc_congestion (tc);
 
   /* Post retransmit update cwnd to ssthresh and account for the
@@ -1310,8 +1286,29 @@ tcp_should_fastrecover_sack (tcp_connection_t * tc)
 }
 
 static inline u8
-tcp_should_fastrecover (tcp_connection_t * tc)
+tcp_should_fastrecover (tcp_connection_t * tc, u8 has_sack)
 {
+  if (!has_sack)
+    {
+      /* If of of the two conditions lower hold, reset dupacks because
+       * we're probably after timeout (RFC6582 heuristics).
+       * If Cumulative ack does not cover more than congestion threshold,
+       * and:
+       * 1) The following doesn't hold: The congestion window is greater
+       *    than SMSS bytes and the difference between highest_ack
+       *    and prev_highest_ack is at most 4*SMSS bytes
+       * 2) Echoed timestamp in the last non-dup ack does not equal the
+       *    stored timestamp
+       */
+      if (seq_leq (tc->snd_una, tc->snd_congestion)
+	  && ((!(tc->cwnd > tc->snd_mss
+		 && tc->bytes_acked <= 4 * tc->snd_mss))
+	      || (tc->rcv_opts.tsecr != tc->tsecr_last_ack)))
+	{
+	  tc->rcv_dupacks = 0;
+	  return 0;
+	}
+    }
   return ((tc->rcv_dupacks == TCP_DUPACK_THRESHOLD)
 	  || tcp_should_fastrecover_sack (tc));
 }
@@ -1330,6 +1327,7 @@ tcp_cc_recover (tcp_connection_t * tc)
       is_spurious = 1;
     }
 
+  tc->rcv_dupacks = 0;
   tc->prr_delivered = 0;
   tc->rxt_delivered = 0;
   tc->snd_rxt_bytes = 0;
@@ -1342,8 +1340,9 @@ tcp_cc_recover (tcp_connection_t * tc)
   if (tc->sack_sb.sacked_bytes)
     {
       tc->snd_congestion = tc->snd_nxt;
-      if (tcp_opts_sack_permitted (&tc->rcv_opts))
-	scoreboard_init_high_rxt (&tc->sack_sb, tc->snd_una);
+      tc->snd_rxt_ts = tcp_tstamp (tc);
+      tc->prr_start = tc->snd_una;
+      scoreboard_init_rxt (&tc->sack_sb, tc->snd_una);
       tcp_program_retransmit (tc);
       return is_spurious;
     }
@@ -1355,6 +1354,8 @@ tcp_cc_recover (tcp_connection_t * tc)
   if (!tcp_in_recovery (tc) && !is_spurious)
     tcp_cc_recovered (tc);
 
+  tcp_connection_tx_pacer_reset (tc, tc->cwnd, 0 /* start bucket */ );
+
   tcp_fastrecovery_off (tc);
   tcp_fastrecovery_first_off (tc);
   tcp_recovery_off (tc);
@@ -1387,30 +1388,6 @@ tcp_cc_update (tcp_connection_t * tc, tcp_rate_sample_t * rs)
     tc->snd_congestion = tc->snd_una - 1;
 }
 
-static void
-tcp_update_delivered (tcp_connection_t * tc, u8 is_dack, u8 has_sack)
-{
-  if (has_sack)
-    {
-      ASSERT (tc->bytes_acked >= tc->sack_sb.last_bytes_delivered
-	      || (tc->flags & TCP_CONN_FINSNT));
-
-      tc->rxt_delivered += tc->sack_sb.rxt_sacked;
-      tc->prr_delivered += tc->bytes_acked + tc->sack_sb.last_sacked_bytes
-	- tc->sack_sb.last_bytes_delivered;
-    }
-  else
-    {
-      tcp_fastrecovery_first_on (tc);
-      tc->rxt_delivered = clib_max (tc->rxt_delivered + tc->bytes_acked,
-				    tc->snd_rxt_bytes);
-      if (is_dack)
-	tc->prr_delivered += is_dack;
-      else
-	tc->prr_delivered += tc->bytes_acked - tc->snd_mss * tc->rcv_dupacks;
-    }
-}
-
 /**
  * One function to rule them all ... and in the darkness bind them
  */
@@ -1421,92 +1398,34 @@ tcp_cc_handle_event (tcp_connection_t * tc, tcp_rate_sample_t * rs,
   u8 has_sack = tcp_opts_sack_permitted (&tc->rcv_opts);
 
   /*
-   * Already in fast recovery. Return if no data acked, partial acks
-   * and accounting for segments that have left the network are done
-   * lower.
+   * If not in recovery, figure out if we should enter
    */
-  if (tcp_in_cong_recovery (tc))
+  if (!tcp_in_cong_recovery (tc))
     {
-      if (!has_sack)
-	tc->rcv_dupacks += is_dack;
-
-      if (!tc->bytes_acked)
-	{
-	  tcp_update_delivered (tc, is_dack, has_sack);
-	  tcp_program_retransmit (tc);
-	  if (!has_sack)
-	    tcp_cc_rcv_cong_ack (tc, TCP_CC_DUPACK, rs);
-	  return;
-	}
-    }
-  /*
-   * Duplicate ACK. Check if we should enter fast recovery
-   */
-  else if (is_dack)
-    {
-      TCP_EVT (TCP_EVT_DUPACK_RCVD, tc, 1);
-      ASSERT (tc->snd_una != tc->snd_nxt || tc->sack_sb.last_sacked_bytes);
-
-      /* Heuristic to catch potential late dupacks */
-      if (!tc->sack_sb.sacked_bytes && tc->snd_una == tc->snd_congestion
-	  && timestamp_leq (tc->rcv_opts.tsecr, tc->tsecr_last_ack))
-	return;
+      ASSERT (is_dack);
 
       tc->rcv_dupacks++;
+      TCP_EVT (TCP_EVT_DUPACK_RCVD, tc, 1);
+      tcp_cc_rcv_cong_ack (tc, TCP_CC_DUPACK, rs);
 
-      if (tcp_should_fastrecover (tc))
+      if (tcp_should_fastrecover (tc, has_sack))
 	{
-	  ASSERT (!tcp_in_fastrecovery (tc));
-
 	  tcp_cc_init_congestion (tc);
 
 	  if (has_sack)
-	    scoreboard_init_high_rxt (&tc->sack_sb, tc->snd_una);
+	    scoreboard_init_rxt (&tc->sack_sb, tc->snd_una);
 
 	  tcp_connection_tx_pacer_reset (tc, tc->cwnd, 0 /* start bucket */ );
 	  tcp_program_retransmit (tc);
-	  return;
-	}
-      else
-	{
-	  tcp_cc_rcv_cong_ack (tc, TCP_CC_DUPACK, rs);
-	  return;
-	}
-    }
-  /* Don't allow entry in fast recovery if still in recovery, for now */
-  else if (0 && is_dack && tcp_in_recovery (tc))
-    {
-      /* If of of the two conditions lower hold, reset dupacks because
-       * we're probably after timeout (RFC6582 heuristics).
-       * If Cumulative ack does not cover more than congestion threshold,
-       * and:
-       * 1) The following doesn't hold: The congestion window is greater
-       *    than SMSS bytes and the difference between highest_ack
-       *    and prev_highest_ack is at most 4*SMSS bytes
-       * 2) Echoed timestamp in the last non-dup ack does not equal the
-       *    stored timestamp
-       */
-      if (seq_leq (tc->snd_una, tc->snd_congestion)
-	  && ((!(tc->cwnd > tc->snd_mss
-		 && tc->bytes_acked <= 4 * tc->snd_mss))
-	      || (tc->rcv_opts.tsecr != tc->tsecr_last_ack)))
-	{
-	  tc->rcv_dupacks = 0;
-	  return;
 	}
-    }
 
-  ASSERT (tc->bytes_acked);
-  TCP_EVT (TCP_EVT_CC_PACK, tc);
+      return;
+    }
 
   /*
-   * Legitimate ACK. 1) See if we can exit recovery
+   * Already in recovery. See if we can exit and stop retransmitting
    */
 
-  /* RFC6675: If the incoming ACK is a cumulative acknowledgment,
-   * reset dupacks to 0. Also needed if in congestion recovery */
-  tc->rcv_dupacks = 0;
-
   if (seq_geq (tc->snd_una, tc->snd_congestion))
     {
       /* If spurious return, we've already updated everything */
@@ -1522,21 +1441,88 @@ tcp_cc_handle_event (tcp_connection_t * tc, tcp_rate_sample_t * rs,
     }
 
   /*
-   * Legitimate ACK. 2) If PARTIAL ACK try to retransmit
+   * Process (re)transmit feedback. Output path uses this to decide how much
+   * more data to release into the network
    */
+  if (has_sack)
+    {
+      tc->rxt_delivered += tc->sack_sb.rxt_sacked;
+      tc->prr_delivered += tc->bytes_acked + tc->sack_sb.last_sacked_bytes
+	- tc->sack_sb.last_bytes_delivered;
+
+      tcp_program_retransmit (tc);
+    }
+  else
+    {
+      if (is_dack)
+	{
+	  tc->rcv_dupacks += 1;
+	  TCP_EVT (TCP_EVT_DUPACK_RCVD, tc, 1);
+	}
+      tc->rxt_delivered = clib_max (tc->rxt_delivered + tc->bytes_acked,
+				    tc->snd_rxt_bytes);
+      if (is_dack)
+	tc->prr_delivered += 1;
+      else
+	tc->prr_delivered += tc->bytes_acked - tc->snd_mss * tc->rcv_dupacks;
 
-  /* Remove retransmitted bytes that have been delivered */
-  tcp_update_delivered (tc, is_dack, has_sack);
+      /* If partial ack, assume that the first un-acked segment was lost */
+      if (tc->bytes_acked || tc->rcv_dupacks == TCP_DUPACK_THRESHOLD)
+	tcp_fastrecovery_first_on (tc);
+
+      tcp_program_retransmit (tc);
+    }
+
+  /*
+   * Notify cc of the event
+   */
+
+  if (!tc->bytes_acked)
+    {
+      tcp_cc_rcv_cong_ack (tc, TCP_CC_DUPACK, rs);
+      return;
+    }
+
+  /* RFC6675: If the incoming ACK is a cumulative acknowledgment,
+   * reset dupacks to 0. Also needed if in congestion recovery */
+  tc->rcv_dupacks = 0;
 
   if (tcp_in_recovery (tc))
     tcp_cc_rcv_ack (tc, rs);
   else
     tcp_cc_rcv_cong_ack (tc, TCP_CC_PARTIALACK, rs);
+}
 
-  /*
-   * Since this was a partial ack, try to retransmit some more data
-   */
-  tcp_program_retransmit (tc);
+/**
+ * Check if duplicate ack as per RFC5681 Sec. 2
+ */
+always_inline u8
+tcp_ack_is_dupack (tcp_connection_t * tc, vlib_buffer_t * b, u32 prev_snd_wnd,
+		   u32 prev_snd_una)
+{
+  return ((vnet_buffer (b)->tcp.ack_number == prev_snd_una)
+	  && seq_gt (tc->snd_nxt, tc->snd_una)
+	  && (vnet_buffer (b)->tcp.seq_end == vnet_buffer (b)->tcp.seq_number)
+	  && (prev_snd_wnd == tc->snd_wnd));
+}
+
+/**
+ * Checks if ack is a congestion control event.
+ */
+static u8
+tcp_ack_is_cc_event (tcp_connection_t * tc, vlib_buffer_t * b,
+		     u32 prev_snd_wnd, u32 prev_snd_una, u8 * is_dack)
+{
+  /* Check if ack is duplicate. Per RFC 6675, ACKs that SACK new data are
+   * defined to be 'duplicate' as well */
+  *is_dack = tc->sack_sb.last_sacked_bytes
+    || tcp_ack_is_dupack (tc, b, prev_snd_wnd, prev_snd_una);
+
+  /* If reneging, wait for timer based retransmits */
+  if (PREDICT_FALSE (tcp_is_lost_fin (tc) || tc->sack_sb.is_reneging))
+    return 0;
+
+  return (*is_dack || tcp_in_cong_recovery (tc));
 }
 
 /**