tcp: use sacks for timer based recovery

Type: feature

If available, reuse sack scoreboard in timer triggered retransmit to
minimize spurious retransmits.

Additional changes/refactoring:
- limited transmit updates
- add sacked rxt count to scoreboard
- prr pacing of fast retransmits
- startup pacing updates
- changed loss window to flight + mss

Change-Id: I057de6a9d6401698bd1031d5cf5cfbb62f2bdf61
Signed-off-by: Florin Coras <fcoras@cisco.com>

9 files changed, 337 insertions, 278 deletions

diff --git a/src/vnet/session/transport.c b/src/vnet/session/transport.c
index effd5891e0b..3e723994752 100644
--- a/src/vnet/session/transport.c
+++ b/src/vnet/session/transport.c
@@ -578,7 +578,8 @@ spacer_max_burst (spacer_t * pacer, u64 norm_time_now)
   u64 n_periods = norm_time_now - pacer->last_update;
   u64 inc;
 
-  if (n_periods > 0 && (inc = n_periods * pacer->tokens_per_period) > 10)
+  if (n_periods > 0
+      && (inc = (f32) n_periods * pacer->tokens_per_period) > 10)
     {
       pacer->last_update = norm_time_now;
       pacer->bucket = clib_min (pacer->bucket + inc, pacer->bytes_per_sec);
@@ -608,6 +609,13 @@ spacer_pace_rate (spacer_t * pacer)
   return pacer->bytes_per_sec;
 }
 
+static inline void
+spacer_reset_bucket (spacer_t * pacer, u64 norm_time_now)
+{
+  pacer->last_update = norm_time_now;
+  pacer->bucket = 0;
+}
+
 void
 transport_connection_tx_pacer_reset (transport_connection_t * tc,
 				     u32 rate_bytes_per_sec,
@@ -646,6 +654,14 @@ transport_connection_tx_pacer_burst (transport_connection_t * tc,
   return spacer_max_burst (&tc->pacer, time_now);
 }
 
+void
+transport_connection_tx_pacer_reset_bucket (transport_connection_t * tc,
+					    u64 time_now)
+{
+  time_now >>= SPACER_CPU_TICKS_PER_PERIOD_SHIFT;
+  spacer_reset_bucket (&tc->pacer, time_now);
+}
+
 u32
 transport_connection_snd_space (transport_connection_t * tc, u64 time_now,
 				u16 mss)
diff --git a/src/vnet/session/transport.h b/src/vnet/session/transport.h
index cbe3c36734c..5b45be0a0be 100644
--- a/src/vnet/session/transport.h
+++ b/src/vnet/session/transport.h
@@ -220,6 +220,15 @@ u32 transport_connection_tx_pacer_burst (transport_connection_t * tc,
 u64 transport_connection_tx_pacer_rate (transport_connection_t * tc);
 
 /**
+ * Reset tx pacer bucket
+ *
+ * @param tc		transport connection
+ * @param time_now	current cpu time
+ */
+void transport_connection_tx_pacer_reset_bucket (transport_connection_t * tc,
+						 u64 time_now);
+
+/**
  * Initialize period for tx pacers
  *
  * Defines a unit of time with respect to number of cpu cycles that is to
diff --git a/src/vnet/tcp/tcp.c b/src/vnet/tcp/tcp.c
index 12e241984cf..75a45a448bd 100644
--- a/src/vnet/tcp/tcp.c
+++ b/src/vnet/tcp/tcp.c
@@ -701,17 +701,15 @@ tcp_init_snd_vars (tcp_connection_t * tc)
   tc->snd_una = tc->iss;
   tc->snd_nxt = tc->iss + 1;
   tc->snd_una_max = tc->snd_nxt;
-  tc->srtt = 0;
+  tc->srtt = 100;		/* 100 ms */
 }
 
 void
 tcp_enable_pacing (tcp_connection_t * tc)
 {
-  u32 initial_bucket, byte_rate;
-  initial_bucket = 16 * tc->snd_mss;
-  byte_rate = 2 << 16;
-  transport_connection_tx_pacer_init (&tc->connection, byte_rate,
-				      initial_bucket);
+  u32 byte_rate;
+  byte_rate = tc->cwnd / (tc->srtt * TCP_TICK);
+  transport_connection_tx_pacer_init (&tc->connection, byte_rate, tc->cwnd);
   tc->mrtt_us = (u32) ~ 0;
 }
 
@@ -725,10 +723,11 @@ tcp_connection_init_vars (tcp_connection_t * tc)
   tcp_connection_timers_init (tc);
   tcp_init_mss (tc);
   scoreboard_init (&tc->sack_sb);
-  tcp_cc_init (tc);
   if (tc->state == TCP_STATE_SYN_RCVD)
     tcp_init_snd_vars (tc);
 
+  tcp_cc_init (tc);
+
   if (!tc->c_is_ip4 && ip6_address_is_link_local_unicast (&tc->c_rmt_ip6))
     tcp_add_del_adjacency (tc, 1);
 
@@ -921,7 +920,7 @@ format_tcp_congestion (u8 * s, va_list * args)
   s = format (s, "%U ", format_tcp_congestion_status, tc);
   s = format (s, "algo %s cwnd %u ssthresh %u bytes_acked %u\n",
 	      tc->cc_algo->name, tc->cwnd, tc->ssthresh, tc->bytes_acked);
-  s = format (s, "%Ucc space %u prev_cwnd %u prev_ssthresh %u rtx_bytes %u\n",
+  s = format (s, "%Ucc space %u prev_cwnd %u prev_ssthresh %u rxt_bytes %u\n",
 	      format_white_space, indent, tcp_available_cc_snd_space (tc),
 	      tc->prev_cwnd, tc->prev_ssthresh, tc->snd_rxt_bytes);
   s = format (s, "%Usnd_congestion %u dupack %u limited_transmit %u\n",
@@ -1141,8 +1140,9 @@ format_tcp_scoreboard (u8 * s, va_list * args)
   sack_scoreboard_hole_t *hole;
   u32 indent = format_get_indent (s);
 
-  s = format (s, "sacked_bytes %u last_sacked_bytes %u lost_bytes %u\n",
-	      sb->sacked_bytes, sb->last_sacked_bytes, sb->lost_bytes);
+  s = format (s, "sacked %u last_sacked %u lost %u last_lost %u\n",
+	      sb->sacked_bytes, sb->last_sacked_bytes, sb->lost_bytes,
+	      sb->last_lost_bytes);
   s = format (s, "%Ulast_bytes_delivered %u high_sacked %u is_reneging %u\n",
 	      format_white_space, indent, sb->last_bytes_delivered,
 	      sb->high_sacked - tc->iss, sb->is_reneging);
@@ -1247,7 +1247,7 @@ tcp_round_snd_space (tcp_connection_t * tc, u32 snd_space)
 static inline u32
 tcp_snd_space_inline (tcp_connection_t * tc)
 {
-  int snd_space, snt_limited;
+  int snd_space;
 
   if (PREDICT_FALSE (tcp_in_fastrecovery (tc)
 		     || tc->state == TCP_STATE_CLOSED))
@@ -1255,18 +1255,21 @@ tcp_snd_space_inline (tcp_connection_t * tc)
 
   snd_space = tcp_available_output_snd_space (tc);
 
-  /* If we haven't gotten dupacks or if we did and have gotten sacked
-   * bytes then we can still send as per Limited Transmit (RFC3042) */
-  if (PREDICT_FALSE (tc->rcv_dupacks != 0
-		     && (tcp_opts_sack_permitted (tc)
-			 && tc->sack_sb.last_sacked_bytes == 0)))
+  /* If we got dupacks or sacked bytes but we're not yet in recovery, try
+   * to force the peer to send enough dupacks to start retransmitting as
+   * per Limited Transmit (RFC3042)
+   */
+  if (PREDICT_FALSE (tc->rcv_dupacks != 0 || tc->sack_sb.sacked_bytes))
     {
-      if (tc->rcv_dupacks == 1 && tc->limited_transmit != tc->snd_nxt)
+      if (tc->limited_transmit != tc->snd_nxt
+	  && (seq_lt (tc->limited_transmit, tc->snd_nxt - 2 * tc->snd_mss)
+	      || seq_gt (tc->limited_transmit, tc->snd_nxt)))
 	tc->limited_transmit = tc->snd_nxt;
+
       ASSERT (seq_leq (tc->limited_transmit, tc->snd_nxt));
 
-      snt_limited = tc->snd_nxt - tc->limited_transmit;
-      snd_space = clib_max (2 * tc->snd_mss - snt_limited, 0);
+      int snt_limited = tc->snd_nxt - tc->limited_transmit;
+      snd_space = clib_max ((int) 2 * tc->snd_mss - snt_limited, 0);
     }
   return tcp_round_snd_space (tc, snd_space);
 }
@@ -1360,9 +1363,9 @@ tcp_connection_tx_pacer_reset (tcp_connection_t * tc, u32 window,
 			       u32 start_bucket)
 {
   tcp_worker_ctx_t *wrk = tcp_get_worker (tc->c_thread_index);
-  u32 byte_rate = window / ((f64) TCP_TICK * tc->srtt);
+  f64 srtt = clib_min ((f64) tc->srtt * TCP_TICK, tc->mrtt_us);
   u64 last_time = wrk->vm->clib_time.last_cpu_time;
-  transport_connection_tx_pacer_reset (&tc->connection, byte_rate,
+  transport_connection_tx_pacer_reset (&tc->connection, window / srtt,
 				       start_bucket, last_time);
 }
 
diff --git a/src/vnet/tcp/tcp.h b/src/vnet/tcp/tcp.h
index 227b3f8a856..a1b7d4cbd0d 100644
--- a/src/vnet/tcp/tcp.h
+++ b/src/vnet/tcp/tcp.h
@@ -32,6 +32,7 @@
 #define TCP_MAX_OPTION_SPACE 40
 #define TCP_CC_DATA_SZ 24
 #define TCP_MAX_GSO_SZ 65536
+#define TCP_RXT_MAX_BURST 10
 
 #define TCP_DUPACK_THRESHOLD 	3
 #define TCP_IW_N_SEGMENTS 	10
@@ -111,7 +112,7 @@ extern timer_expiration_handler tcp_timer_retransmit_syn_handler;
   _(DCNT_PENDING, "Disconnect pending")		\
   _(HALF_OPEN_DONE, "Half-open completed")	\
   _(FINPNDG, "FIN pending")			\
-  _(FRXT_PENDING, "Fast-retransmit pending")	\
+  _(RXT_PENDING, "Retransmit pending")		\
   _(FRXT_FIRST, "Fast-retransmit first again")	\
   _(DEQ_PENDING, "Pending dequeue acked")	\
   _(PSH_PENDING, "PSH pending")			\
@@ -166,6 +167,7 @@ typedef struct _sack_scoreboard
   u32 sacked_bytes;			/**< Number of bytes sacked in sb */
   u32 last_sacked_bytes;		/**< Number of bytes last sacked */
   u32 last_bytes_delivered;		/**< Sack bytes delivered to app */
+  u32 rxt_sacked;			/**< Rxt last delivered */
   u32 high_sacked;			/**< Highest byte sacked (fack) */
   u32 high_rxt;				/**< Highest retransmitted sequence */
   u32 rescue_rxt;			/**< Rescue sequence number */
@@ -219,8 +221,11 @@ sack_scoreboard_hole_t *scoreboard_prev_hole (sack_scoreboard_t * sb,
 					      sack_scoreboard_hole_t * hole);
 sack_scoreboard_hole_t *scoreboard_first_hole (sack_scoreboard_t * sb);
 sack_scoreboard_hole_t *scoreboard_last_hole (sack_scoreboard_t * sb);
+
 void scoreboard_clear (sack_scoreboard_t * sb);
+void scoreboard_clear_reneging (sack_scoreboard_t * sb, u32 start, u32 end);
 void scoreboard_init (sack_scoreboard_t * sb);
+void scoreboard_init_high_rxt (sack_scoreboard_t * sb, u32 snd_una);
 u8 *format_tcp_scoreboard (u8 * s, va_list * args);
 
 #define TCP_BTS_INVALID_INDEX	((u32)~0)
@@ -360,8 +365,10 @@ typedef struct _tcp_connection
   u32 prev_cwnd;	/**< ssthresh before congestion */
   u32 bytes_acked;	/**< Bytes acknowledged by current segment */
   u32 burst_acked;	/**< Bytes acknowledged in current burst */
-  u32 snd_rxt_bytes;	/**< Retransmitted bytes */
+  u32 snd_rxt_bytes;	/**< Retransmitted bytes during current cc event */
   u32 snd_rxt_ts;	/**< Timestamp when first packet is retransmitted */
+  u32 prr_delivered;	/**< RFC6937 bytes delivered during current event */
+  u32 rxt_delivered;	/**< Rxt bytes delivered during current cc event */
   u32 tsecr_last_ack;	/**< Timestamp echoed to us in last healthy ACK */
   u32 snd_congestion;	/**< snd_una_max when congestion is detected */
   u32 tx_fifo_size;	/**< Tx fifo size. Used to constrain cwnd */
@@ -757,7 +764,7 @@ void tcp_send_window_update_ack (tcp_connection_t * tc);
 
 void tcp_program_ack (tcp_connection_t * tc);
 void tcp_program_dupack (tcp_connection_t * tc);
-void tcp_program_fastretransmit (tcp_connection_t * tc);
+void tcp_program_retransmit (tcp_connection_t * tc);
 
 /*
  * Rate estimation
@@ -857,18 +864,9 @@ tcp_flight_size (const tcp_connection_t * tc)
   int flight_size;
 
   flight_size = (int) (tc->snd_nxt - tc->snd_una) - tcp_bytes_out (tc)
-    + tc->snd_rxt_bytes;
+    + tc->snd_rxt_bytes - tc->rxt_delivered;
 
-  if (flight_size < 0)
-    {
-      if (0)
-	clib_warning
-	  ("Negative: %u %u %u dupacks %u sacked bytes %u flags %d",
-	   tc->snd_una_max - tc->snd_una, tcp_bytes_out (tc),
-	   tc->snd_rxt_bytes, tc->rcv_dupacks, tc->sack_sb.sacked_bytes,
-	   tc->rcv_opts.flags);
-      return 0;
-    }
+  ASSERT (flight_size >= 0);
 
   return flight_size;
 }
@@ -912,7 +910,8 @@ tcp_cwnd_accumulate (tcp_connection_t * tc, u32 thresh, u32 bytes)
 always_inline u32
 tcp_loss_wnd (const tcp_connection_t * tc)
 {
-  return tc->snd_mss;
+  /* Whatever we have in flight + the packet we're about to send */
+  return tcp_flight_size (tc) + tc->snd_mss;
 }
 
 always_inline u32
@@ -951,22 +950,14 @@ tcp_available_cc_snd_space (const tcp_connection_t * tc)
 always_inline u8
 tcp_is_lost_fin (tcp_connection_t * tc)
 {
-  if ((tc->flags & TCP_CONN_FINSNT) && tc->snd_una_max - tc->snd_una == 1)
+  if ((tc->flags & TCP_CONN_FINSNT) && (tc->snd_una_max - tc->snd_una == 1))
     return 1;
   return 0;
 }
 
 u32 tcp_snd_space (tcp_connection_t * tc);
-int tcp_retransmit_first_unacked (tcp_worker_ctx_t * wrk,
-				  tcp_connection_t * tc);
-int tcp_fast_retransmit_no_sack (tcp_worker_ctx_t * wrk,
-				 tcp_connection_t * tc, u32 burst_size);
-int tcp_fast_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-			      u32 burst_size);
-int tcp_fast_retransmit (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-			 u32 burst_size);
-void tcp_cc_init_congestion (tcp_connection_t * tc);
-void tcp_cc_fastrecovery_clear (tcp_connection_t * tc);
+//void tcp_cc_init_congestion (tcp_connection_t * tc);
+//void tcp_cc_fastrecovery_clear (tcp_connection_t * tc);
 
 fib_node_index_t tcp_lookup_rmt_in_fib (tcp_connection_t * tc);
 
@@ -1036,6 +1027,12 @@ tcp_cc_rcv_cong_ack (tcp_connection_t * tc, tcp_cc_ack_t ack_type,
 }
 
 static inline void
+tcp_cc_congestion (tcp_connection_t * tc)
+{
+  tc->cc_algo->congestion (tc);
+}
+
+static inline void
 tcp_cc_loss (tcp_connection_t * tc)
 {
   tc->cc_algo->loss (tc);
@@ -1068,9 +1065,10 @@ tcp_cc_get_pacing_rate (tcp_connection_t * tc)
     return tc->cc_algo->get_pacing_rate (tc);
 
   f64 srtt = clib_min ((f64) tc->srtt * TCP_TICK, tc->mrtt_us);
+
   /* TODO should constrain to interface's max throughput but
    * we don't have link speeds for sw ifs ..*/
-  return (tc->cwnd / srtt);
+  return ((f64) tc->cwnd / srtt);
 }
 
 always_inline void
diff --git a/src/vnet/tcp/tcp_cubic.c b/src/vnet/tcp/tcp_cubic.c
index aa318961533..17f7932ea2e 100644
--- a/src/vnet/tcp/tcp_cubic.c
+++ b/src/vnet/tcp/tcp_cubic.c
@@ -103,10 +103,7 @@ cubic_congestion (tcp_connection_t * tc)
 
   cd->w_max = w_max;
   tc->ssthresh = clib_max (tc->cwnd * beta_cubic, 2 * tc->snd_mss);
-
   tc->cwnd = tc->ssthresh;
-  if (!tcp_opts_sack_permitted (&tc->rcv_opts))
-    tc->cwnd += 3 * tc->snd_mss;
 }
 
 static void
@@ -114,11 +111,10 @@ cubic_loss (tcp_connection_t * tc)
 {
   cubic_data_t *cd = (cubic_data_t *) tcp_cc_data (tc);
 
-  tc->ssthresh = clib_max (tc->cwnd * beta_cubic, 2 * tc->snd_mss);
   tc->cwnd = tcp_loss_wnd (tc);
   cd->t_start = cubic_time (tc->c_thread_index);
   cd->K = 0;
-  cd->w_max = 0;
+  cd->w_max = tc->cwnd / tc->snd_mss;
 }
 
 static void
@@ -159,7 +155,7 @@ cubic_rcv_ack (tcp_connection_t * tc, tcp_rate_sample_t * rs)
 
   if (tcp_in_slowstart (tc))
     {
-      tc->cwnd += clib_min (tc->snd_mss, tc->bytes_acked);
+      tc->cwnd += tc->bytes_acked;
       return;
     }
 
diff --git a/src/vnet/tcp/tcp_input.c b/src/vnet/tcp/tcp_input.c
index 933f913bc5a..b49b8e8fd77 100755
--- a/src/vnet/tcp/tcp_input.c
+++ b/src/vnet/tcp/tcp_input.c
@@ -508,8 +508,6 @@ tcp_update_rtt (tcp_connection_t * tc, tcp_rate_sample_t * rs, u32 ack)
 	  mrtt = rs->rtt_time * THZ;
 	  goto estimate_rtt;
 	}
-      if (tcp_in_recovery (tc))
-	return 0;
       goto done;
     }
 
@@ -784,9 +782,17 @@ scoreboard_insert_hole (sack_scoreboard_t * sb, u32 prev_index,
 
   return hole;
 }
-#endif /* CLIB_MARCH_VARIANT */
 
-#ifndef CLIB_MARCH_VARIANT
+always_inline void
+scoreboard_update_sacked_rxt (sack_scoreboard_t * sb, u32 start, u32 end,
+			      u8 has_rxt)
+{
+  if (!has_rxt || seq_geq (start, sb->high_rxt))
+    return;
+
+  sb->rxt_sacked +=
+    seq_lt (end, sb->high_rxt) ? (end - start) : (sb->high_rxt - start);
+}
 
 always_inline void
 scoreboard_update_bytes (sack_scoreboard_t * sb, u32 ack, u32 snd_mss)
@@ -837,7 +843,7 @@ scoreboard_update_bytes (sack_scoreboard_t * sb, u32 ack, u32 snd_mss)
   while (right)
     {
       sb->lost_bytes += scoreboard_hole_bytes (right);
-      sb->last_lost_bytes += right->is_lost ? 0 : right->end - right->start;
+      sb->last_lost_bytes += right->is_lost ? 0 : (right->end - right->start);
       right->is_lost = 1;
       left = scoreboard_prev_hole (sb, right);
       if (!left)
@@ -912,9 +918,8 @@ scoreboard_next_rxt_hole (sack_scoreboard_t * sb,
 
   return hole;
 }
-#endif /* CLIB_MARCH_VARIANT */
 
-static void
+void
 scoreboard_init_high_rxt (sack_scoreboard_t * sb, u32 snd_una)
 {
   sack_scoreboard_hole_t *hole;
@@ -928,7 +933,6 @@ scoreboard_init_high_rxt (sack_scoreboard_t * sb, u32 snd_una)
   sb->rescue_rxt = snd_una - 1;
 }
 
-#ifndef  CLIB_MARCH_VARIANT
 void
 scoreboard_init (sack_scoreboard_t * sb)
 {
@@ -957,6 +961,23 @@ scoreboard_clear (sack_scoreboard_t * sb)
   sb->cur_rxt_hole = TCP_INVALID_SACK_HOLE_INDEX;
   sb->is_reneging = 0;
 }
+
+void
+scoreboard_clear_reneging (sack_scoreboard_t * sb, u32 start, u32 end)
+{
+  sack_scoreboard_hole_t *last_hole;
+
+  clib_warning ("sack reneging");
+
+  scoreboard_clear (sb);
+  last_hole = scoreboard_insert_hole (sb, TCP_INVALID_SACK_HOLE_INDEX,
+				      start, end);
+  last_hole->is_lost = 1;
+  sb->tail = scoreboard_hole_index (sb, last_hole);
+  sb->high_sacked = start;
+  scoreboard_init_high_rxt (sb, start);
+}
+
 #endif /* CLIB_MARCH_VARIANT */
 
 /**
@@ -983,14 +1004,18 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
   sack_scoreboard_t *sb = &tc->sack_sb;
   sack_block_t *blk, *rcv_sacks;
   u32 blk_index = 0, i, j;
+  u8 has_rxt;
 
   sb->last_sacked_bytes = 0;
   sb->last_bytes_delivered = 0;
+  sb->rxt_sacked = 0;
 
   if (!tcp_opts_sack (&tc->rcv_opts)
       && sb->head == TCP_INVALID_SACK_HOLE_INDEX)
     return;
 
+  has_rxt = tcp_in_cong_recovery (tc);
+
   /* Remove invalid blocks */
   blk = tc->rcv_opts.sacks;
   while (blk < vec_end (tc->rcv_opts.sacks))
@@ -1121,6 +1146,8 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
 		      sb->is_reneging = 0;
 		    }
 		}
+	      scoreboard_update_sacked_rxt (sb, hole->start, hole->end,
+					    has_rxt);
 	      scoreboard_remove_hole (sb, hole);
 	      hole = next_hole;
 	    }
@@ -1129,6 +1156,8 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
 	    {
 	      if (seq_gt (blk->end, hole->start))
 		{
+		  scoreboard_update_sacked_rxt (sb, hole->start, blk->end,
+						has_rxt);
 		  hole->start = blk->end;
 		}
 	      blk_index++;
@@ -1145,11 +1174,17 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
 	      /* Pool might've moved */
 	      hole = scoreboard_get_hole (sb, hole_index);
 	      hole->end = blk->start;
+
+	      scoreboard_update_sacked_rxt (sb, blk->start, blk->end,
+					    has_rxt);
+
 	      blk_index++;
 	      ASSERT (hole->next == scoreboard_hole_index (sb, next_hole));
 	    }
 	  else if (seq_lt (blk->start, hole->end))
 	    {
+	      scoreboard_update_sacked_rxt (sb, blk->start, hole->end,
+					    has_rxt);
 	      hole->end = blk->start;
 	    }
 	  hole = scoreboard_next_hole (sb, hole);
@@ -1166,6 +1201,8 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
   ASSERT (sb->head == TCP_INVALID_SACK_HOLE_INDEX || tcp_in_recovery (tc)
 	  || sb->is_reneging || sb->holes[sb->head].start == 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);
 
   TCP_EVT (TCP_EVT_CC_SCOREBOARD, tc);
 }
@@ -1209,70 +1246,41 @@ tcp_update_snd_wnd (tcp_connection_t * tc, u32 seq, u32 ack, u32 snd_wnd)
     }
 }
 
-#ifndef CLIB_MARCH_VARIANT
 /**
  * Init loss recovery/fast recovery.
  *
  * Triggered by dup acks as opposed to timer timeout. Note that cwnd is
  * updated in @ref tcp_cc_handle_event after fast retransmit
  */
-void
+static void
 tcp_cc_init_congestion (tcp_connection_t * tc)
 {
   tcp_fastrecovery_on (tc);
   tc->snd_congestion = tc->snd_nxt;
   tc->cwnd_acc_bytes = 0;
   tc->snd_rxt_bytes = 0;
+  tc->rxt_delivered = 0;
+  tc->prr_delivered = 0;
   tc->prev_ssthresh = tc->ssthresh;
   tc->prev_cwnd = tc->cwnd;
-  tc->cc_algo->congestion (tc);
-  tc->fr_occurences += 1;
-  TCP_EVT (TCP_EVT_CC_EVT, tc, 4);
-}
-#endif /* CLIB_MARCH_VARIANT */
 
-static void
-tcp_cc_recovery_exit (tcp_connection_t * tc)
-{
-  tc->rto_boff = 0;
-  tcp_update_rto (tc);
-  tc->snd_rxt_ts = 0;
-  tc->rtt_ts = 0;
-  tcp_recovery_off (tc);
-  TCP_EVT (TCP_EVT_CC_EVT, tc, 3);
-}
+  tcp_cc_congestion (tc);
 
-#ifndef CLIB_MARCH_VARIANT
-void
-tcp_cc_fastrecovery_clear (tcp_connection_t * tc)
-{
-  tc->snd_rxt_bytes = 0;
-  tc->rcv_dupacks = 0;
-  tc->rtt_ts = 0;
+  /* Post retransmit update cwnd to ssthresh and account for the
+   * three segments that have left the network and should've been
+   * buffered at the receiver XXX */
+  if (!tcp_opts_sack_permitted (&tc->rcv_opts))
+    tc->cwnd += 3 * tc->snd_mss;
 
-  tcp_fastrecovery_off (tc);
-  tcp_fastrecovery_first_off (tc);
-  tc->flags &= ~TCP_CONN_FRXT_PENDING;
-
-  TCP_EVT (TCP_EVT_CC_EVT, tc, 3);
+  tc->fr_occurences += 1;
+  TCP_EVT (TCP_EVT_CC_EVT, tc, 4);
 }
-#endif /* CLIB_MARCH_VARIANT */
 
 static void
 tcp_cc_congestion_undo (tcp_connection_t * tc)
 {
   tc->cwnd = tc->prev_cwnd;
   tc->ssthresh = tc->prev_ssthresh;
-  tc->rcv_dupacks = 0;
-  if (tcp_in_recovery (tc))
-    {
-      tcp_cc_recovery_exit (tc);
-      tc->snd_nxt = seq_max (tc->snd_nxt, tc->snd_congestion);
-    }
-  else if (tcp_in_fastrecovery (tc))
-    {
-      tcp_cc_fastrecovery_clear (tc);
-    }
   tcp_cc_undo_recovery (tc);
   ASSERT (tc->rto_boff == 0);
   TCP_EVT (TCP_EVT_CC_EVT, tc, 5);
@@ -1288,48 +1296,74 @@ tcp_cc_is_spurious_timeout_rxt (tcp_connection_t * tc)
 }
 
 static inline u8
-tcp_cc_is_spurious_fast_rxt (tcp_connection_t * tc)
+tcp_cc_is_spurious_retransmit (tcp_connection_t * tc)
 {
-  return (tcp_in_fastrecovery (tc)
-	  && tc->cwnd > tc->ssthresh + 3 * tc->snd_mss);
+  return (tcp_cc_is_spurious_timeout_rxt (tc));
 }
 
-static u8
-tcp_cc_is_spurious_retransmit (tcp_connection_t * tc)
+static inline u8
+tcp_should_fastrecover_sack (tcp_connection_t * tc)
+{
+  return (tc->sack_sb.lost_bytes
+	  || ((TCP_DUPACK_THRESHOLD - 1) * tc->snd_mss
+	      < tc->sack_sb.sacked_bytes));
+}
+
+static inline u8
+tcp_should_fastrecover (tcp_connection_t * tc)
 {
-  return (tcp_cc_is_spurious_timeout_rxt (tc)
-	  || tcp_cc_is_spurious_fast_rxt (tc));
+  return ((tc->rcv_dupacks == TCP_DUPACK_THRESHOLD)
+	  || tcp_should_fastrecover_sack (tc));
 }
 
 static int
 tcp_cc_recover (tcp_connection_t * tc)
 {
   sack_scoreboard_hole_t *hole;
+  u8 is_spurious = 0;
 
   ASSERT (tcp_in_cong_recovery (tc));
 
-  hole = scoreboard_first_hole (&tc->sack_sb);
-  if (hole && hole->start == tc->snd_una && hole->end == tc->snd_nxt)
-    scoreboard_clear (&tc->sack_sb);
-
   if (tcp_cc_is_spurious_retransmit (tc))
     {
       tcp_cc_congestion_undo (tc);
-      return 1;
+      is_spurious = 1;
     }
 
-  if (tcp_in_recovery (tc))
-    tcp_cc_recovery_exit (tc);
-  else if (tcp_in_fastrecovery (tc))
+  tc->prr_delivered = 0;
+  tc->rxt_delivered = 0;
+  tc->snd_rxt_bytes = 0;
+  tc->snd_rxt_ts = 0;
+  tc->rtt_ts = 0;
+  tc->flags &= ~TCP_CONN_RXT_PENDING;
+
+  /* Previous recovery left us congested. Continue sending as part
+   * of the current recovery event with an updated snd_congestion */
+  if (tc->sack_sb.sacked_bytes)
     {
-      tcp_cc_recovered (tc);
-      tcp_cc_fastrecovery_clear (tc);
+      tc->snd_congestion = tc->snd_nxt;
+      if (tcp_opts_sack_permitted (&tc->rcv_opts))
+	scoreboard_init_high_rxt (&tc->sack_sb, tc->snd_una);
+      tcp_program_retransmit (tc);
+      return is_spurious;
     }
 
+  hole = scoreboard_first_hole (&tc->sack_sb);
+  if (hole && hole->start == tc->snd_una && hole->end == tc->snd_nxt)
+    scoreboard_clear (&tc->sack_sb);
+
+  if (!tcp_in_recovery (tc) && !is_spurious)
+    tcp_cc_recovered (tc);
+
+  tcp_fastrecovery_off (tc);
+  tcp_fastrecovery_first_off (tc);
+  tcp_recovery_off (tc);
+  TCP_EVT (TCP_EVT_CC_EVT, tc, 3);
+
   ASSERT (tc->rto_boff == 0);
   ASSERT (!tcp_in_cong_recovery (tc));
   ASSERT (tcp_scoreboard_is_sane_post_recovery (tc));
-  return 0;
+  return is_spurious;
 }
 
 static void
@@ -1353,17 +1387,28 @@ tcp_cc_update (tcp_connection_t * tc, tcp_rate_sample_t * rs)
     tc->snd_congestion = tc->snd_una - 1;
 }
 
-static u8
-tcp_should_fastrecover_sack (tcp_connection_t * tc)
+static void
+tcp_update_delivered (tcp_connection_t * tc, u8 is_dack, u8 has_sack)
 {
-  return (TCP_DUPACK_THRESHOLD - 1) * tc->snd_mss < tc->sack_sb.sacked_bytes;
-}
+  if (has_sack)
+    {
+      ASSERT (tc->bytes_acked >= tc->sack_sb.last_bytes_delivered
+	      || (tc->flags & TCP_CONN_FINSNT));
 
-static u8
-tcp_should_fastrecover (tcp_connection_t * tc)
-{
-  return (tc->rcv_dupacks == TCP_DUPACK_THRESHOLD
-	  || tcp_should_fastrecover_sack (tc));
+      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;
+    }
 }
 
 /**
@@ -1380,29 +1425,21 @@ tcp_cc_handle_event (tcp_connection_t * tc, tcp_rate_sample_t * rs,
    * and accounting for segments that have left the network are done
    * lower.
    */
-  if (tcp_in_fastrecovery (tc))
+  if (tcp_in_cong_recovery (tc))
     {
       if (!has_sack)
-	tc->rcv_dupacks++;
+	tc->rcv_dupacks += is_dack;
 
       if (!tc->bytes_acked)
 	{
-	  tcp_program_fastretransmit (tc);
+	  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;
 	}
     }
   /*
-   * In timer triggered recovery
-   */
-  else if (tcp_in_recovery (tc))
-    {
-      /* No fast recovery entry at this point */
-      if (!tc->bytes_acked)
-	return;
-    }
-  /*
    * Duplicate ACK. Check if we should enter fast recovery
    */
   else if (is_dack)
@@ -1410,33 +1447,24 @@ tcp_cc_handle_event (tcp_connection_t * tc, tcp_rate_sample_t * rs,
       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;
+
       tc->rcv_dupacks++;
 
       if (tcp_should_fastrecover (tc))
 	{
-	  u32 pacer_wnd;
-
 	  ASSERT (!tcp_in_fastrecovery (tc));
 
-	  /* Heuristic to catch potential late dupacks
-	   * after fast retransmit exits */
-	  if (is_dack && tc->snd_una == tc->snd_congestion
-	      && timestamp_leq (tc->rcv_opts.tsecr, tc->tsecr_last_ack))
-	    {
-	      tc->rcv_dupacks = 0;
-	      return;
-	    }
-
 	  tcp_cc_init_congestion (tc);
 
 	  if (has_sack)
 	    scoreboard_init_high_rxt (&tc->sack_sb, tc->snd_una);
 
-	  /* Constrain rate until we get a partial ack */
-	  pacer_wnd = clib_max (0.1 * tc->cwnd, 2 * tc->snd_mss);
-	  tcp_connection_tx_pacer_reset (tc, pacer_wnd,
-					 0 /* start bucket */ );
-	  tcp_program_fastretransmit (tc);
+	  tcp_connection_tx_pacer_reset (tc, tc->cwnd, 0 /* start bucket */ );
+	  tcp_program_retransmit (tc);
 	  return;
 	}
       else
@@ -1475,6 +1503,10 @@ tcp_cc_handle_event (tcp_connection_t * tc, tcp_rate_sample_t * rs,
    * Legitimate ACK. 1) See if we can exit recovery
    */
 
+  /* 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 */
@@ -1493,55 +1525,18 @@ tcp_cc_handle_event (tcp_connection_t * tc, tcp_rate_sample_t * rs,
    * Legitimate ACK. 2) If PARTIAL ACK try to retransmit
    */
 
-  /* RFC6675: If the incoming ACK is a cumulative acknowledgment,
-   * reset dupacks to 0. Also needed if in congestion recovery */
-  tc->rcv_dupacks = 0;
-
-  /* Post RTO timeout don't try anything fancy */
-  if (tcp_in_recovery (tc))
-    {
-      tcp_cc_rcv_ack (tc, rs);
-      transport_add_tx_event (&tc->connection);
-      return;
-    }
-
   /* Remove retransmitted bytes that have been delivered */
-  if (has_sack)
-    {
-      ASSERT (tc->bytes_acked >= tc->sack_sb.last_bytes_delivered
-	      || (tc->flags & TCP_CONN_FINSNT));
+  tcp_update_delivered (tc, is_dack, has_sack);
 
-      /* If we have sacks and we haven't gotten an ack beyond high_rxt,
-       * remove sacked bytes delivered */
-      if (seq_lt (tc->snd_una, tc->sack_sb.high_rxt))
-	{
-	  u32 rxt_delivered;
-	  rxt_delivered = tc->bytes_acked - tc->sack_sb.last_bytes_delivered;
-	  ASSERT (tc->snd_rxt_bytes >= rxt_delivered);
-	  tc->snd_rxt_bytes -= rxt_delivered;
-	}
-      else
-	{
-	  /* Apparently all retransmitted holes have been acked */
-	  tc->snd_rxt_bytes = 0;
-	  tc->sack_sb.high_rxt = tc->snd_una;
-	}
-    }
+  if (tcp_in_recovery (tc))
+    tcp_cc_rcv_ack (tc, rs);
   else
-    {
-      tcp_fastrecovery_first_on (tc);
-      if (tc->snd_rxt_bytes > tc->bytes_acked)
-	tc->snd_rxt_bytes -= tc->bytes_acked;
-      else
-	tc->snd_rxt_bytes = 0;
-    }
-
-  tcp_cc_rcv_cong_ack (tc, TCP_CC_PARTIALACK, rs);
+    tcp_cc_rcv_cong_ack (tc, TCP_CC_PARTIALACK, rs);
 
   /*
    * Since this was a partial ack, try to retransmit some more data
    */
-  tcp_program_fastretransmit (tc);
+  tcp_program_retransmit (tc);
 }
 
 /**
@@ -2767,6 +2762,7 @@ tcp46_rcv_process_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
 
 	  /* Update rtt and rto */
 	  tcp_estimate_initial_rtt (tc0);
+	  tcp_connection_tx_pacer_update (tc0);
 
 	  /* Switch state to ESTABLISHED */
 	  tc0->state = TCP_STATE_ESTABLISHED;
diff --git a/src/vnet/tcp/tcp_newreno.c b/src/vnet/tcp/tcp_newreno.c
index 8b704a6ba04..e9213a2e6d9 100644
--- a/src/vnet/tcp/tcp_newreno.c
+++ b/src/vnet/tcp/tcp_newreno.c
@@ -20,17 +20,11 @@ newreno_congestion (tcp_connection_t * tc)
 {
   tc->ssthresh = clib_max (tcp_flight_size (tc) / 2, 2 * tc->snd_mss);
   tc->cwnd = tc->ssthresh;
-  /* Post retransmit update cwnd to ssthresh and account for the
-   * three segments that have left the network and should've been
-   * buffered at the receiver XXX */
-  if (!tcp_opts_sack_permitted (&tc->rcv_opts))
-    tc->cwnd += 3 * tc->snd_mss;
 }
 
 static void
 newreno_loss (tcp_connection_t * tc)
 {
-  tc->ssthresh = clib_max (tcp_flight_size (tc) / 2, 2 * tc->snd_mss);
   tc->cwnd = tcp_loss_wnd (tc);
 }
 
diff --git a/src/vnet/tcp/tcp_output.c b/src/vnet/tcp/tcp_output.c
index 15aa85712e3..069b823ee36 100644
--- a/src/vnet/tcp/tcp_output.c
+++ b/src/vnet/tcp/tcp_output.c
@@ -1159,12 +1159,12 @@ tcp_program_dupack (tcp_connection_t * tc)
 }
 
 void
-tcp_program_fastretransmit (tcp_connection_t * tc)
+tcp_program_retransmit (tcp_connection_t * tc)
 {
-  if (!(tc->flags & TCP_CONN_FRXT_PENDING))
+  if (!(tc->flags & TCP_CONN_RXT_PENDING))
     {
       session_add_self_custom_tx_evt (&tc->connection, 0);
-      tc->flags |= TCP_CONN_FRXT_PENDING;
+      tc->flags |= TCP_CONN_RXT_PENDING;
     }
 }
 
@@ -1369,19 +1369,31 @@ tcp_prepare_retransmit_segment (tcp_worker_ctx_t * wrk,
   if (!n_bytes)
     return 0;
 
-  if (tcp_in_fastrecovery (tc))
-    {
-      tc->snd_rxt_bytes += n_bytes;
-      if (tc->flags & TCP_CONN_RATE_SAMPLE)
-	tcp_bt_track_rxt (tc, start, start + n_bytes);
-    }
+  tc->snd_rxt_bytes += n_bytes;
+
+  if (tc->flags & TCP_CONN_RATE_SAMPLE)
+    tcp_bt_track_rxt (tc, start, start + n_bytes);
 
   tc->bytes_retrans += n_bytes;
   tc->segs_retrans += 1;
   TCP_EVT (TCP_EVT_CC_RTX, tc, offset, n_bytes);
+
   return n_bytes;
 }
 
+static void
+tcp_check_sack_reneging (tcp_connection_t * tc)
+{
+  sack_scoreboard_t *sb = &tc->sack_sb;
+  sack_scoreboard_hole_t *hole;
+
+  hole = scoreboard_first_hole (sb);
+  if (!sb->is_reneging && (!hole || hole->start == tc->snd_una))
+    return;
+
+  scoreboard_clear_reneging (sb, tc->snd_una, tc->snd_nxt);
+}
+
 /**
  * Reset congestion control, switch cwnd to loss window and try again.
  */
@@ -1389,23 +1401,21 @@ static void
 tcp_cc_init_rxt_timeout (tcp_connection_t * tc)
 {
   TCP_EVT (TCP_EVT_CC_EVT, tc, 6);
+
   tc->prev_ssthresh = tc->ssthresh;
   tc->prev_cwnd = tc->cwnd;
 
-  /* Clear fast recovery state if needed */
-  if (tcp_in_fastrecovery (tc))
-    tcp_cc_fastrecovery_clear (tc);
+  /* If we entrered loss without fast recovery, notify cc algo of the
+   * congestion event such that it can update ssthresh and its state */
+  if (!tcp_in_fastrecovery (tc))
+    tcp_cc_congestion (tc);
 
-  /* Let cc algo decide loss cwnd and ssthresh */
+  /* Let cc algo decide loss cwnd and ssthresh post unrecovered loss */
   tcp_cc_loss (tc);
 
-  /* Start again from the beginning */
-  tc->snd_congestion = tc->snd_nxt;
-  tc->rcv_dupacks = 0;
   tc->rtt_ts = 0;
   tc->cwnd_acc_bytes = 0;
   tc->tr_occurences += 1;
-  tcp_connection_tx_pacer_reset (tc, tc->cwnd, 2 * tc->snd_mss);
   tcp_recovery_on (tc);
 }
 
@@ -1476,29 +1486,14 @@ tcp_timer_retransmit_handler (u32 tc_index)
 	  return;
 	}
 
-      /* Increment RTO backoff (also equal to number of retries) and go back
-       * to first un-acked byte  */
-      tc->rto_boff += 1;
+      if (tcp_opts_sack_permitted (&tc->rcv_opts))
+	tcp_check_sack_reneging (tc);
 
-      /* TODO be less aggressive about clearing scoreboard */
-      scoreboard_clear (&tc->sack_sb);
+      /* Update send congestion to make sure that rxt has data to send */
+      tc->snd_congestion = tc->snd_nxt;
 
-      /* First retransmit timeout */
-      if (tc->rto_boff == 1)
-	{
-	  tcp_cc_init_rxt_timeout (tc);
-	  /* Record timestamp. Eifel detection algorithm RFC3522 */
-	  tc->snd_rxt_ts = tcp_tstamp (tc);
-	}
-
-      if (tc->flags & TCP_CONN_RATE_SAMPLE)
-	tcp_bt_flush_samples (tc);
-
-      /* If we've sent beyond snd_congestion, update it */
-      tc->snd_congestion = seq_max (tc->snd_nxt, tc->snd_congestion);
-      tc->snd_nxt = tc->snd_una;
-
-      /* Send one segment. n_bytes may be zero due to buffer shortfall */
+      /* Send the first unacked segment. If we're short on buffers, return
+       * as soon as possible */
       n_bytes = tcp_prepare_retransmit_segment (wrk, tc, 0, tc->snd_mss, &b);
       if (!n_bytes)
 	{
@@ -1511,6 +1506,19 @@ tcp_timer_retransmit_handler (u32 tc_index)
 
       tc->rto = clib_min (tc->rto << 1, TCP_RTO_MAX);
       tcp_retransmit_timer_force_update (tc);
+
+      tc->rto_boff += 1;
+      if (tc->rto_boff == 1)
+	{
+	  tcp_cc_init_rxt_timeout (tc);
+	  /* Record timestamp. Eifel detection algorithm RFC3522 */
+	  tc->snd_rxt_ts = tcp_tstamp (tc);
+	}
+
+      if (tcp_opts_sack_permitted (&tc->rcv_opts))
+	scoreboard_init_high_rxt (&tc->sack_sb, tc->snd_una + tc->snd_mss);
+
+      tcp_program_retransmit (tc);
     }
   /* Retransmit SYN-ACK */
   else if (tc->state == TCP_STATE_SYN_RCVD)
@@ -1728,8 +1736,8 @@ tcp_retransmit_first_unacked (tcp_worker_ctx_t * wrk, tcp_connection_t * tc)
 }
 
 static int
-tcp_fast_retransmit_unsent (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-			    u32 burst_size)
+tcp_transmit_unsent (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
+		     u32 burst_size)
 {
   u32 offset, n_segs = 0, n_written, bi, available_wnd;
   vlib_main_t *vm = wrk->vm;
@@ -1758,18 +1766,44 @@ done:
   return n_segs;
 }
 
+/**
+ * Estimate send space using proportional rate reduction (RFC6937)
+ */
+static int
+tcp_fastrecovery_prr_snd_space (tcp_connection_t * tc)
+{
+  u32 pipe, prr_out;
+  int space;
+
+  pipe = tcp_flight_size (tc);
+  prr_out = tc->snd_rxt_bytes + (tc->snd_nxt - tc->snd_congestion);
+
+  if (pipe > tc->ssthresh)
+    {
+      space = ((int) tc->prr_delivered * ((f64) tc->ssthresh / tc->prev_cwnd))
+	- prr_out;
+    }
+  else
+    {
+      int limit = tc->prr_delivered - prr_out + tc->snd_mss;
+      space = clib_min (tc->ssthresh - pipe, limit);
+    }
+  space = clib_max (space, prr_out ? 0 : tc->snd_mss);
+  return space;
+}
+
 #define scoreboard_rescue_rxt_valid(_sb, _tc)			\
     (seq_geq (_sb->rescue_rxt, _tc->snd_una) 			\
 	&& seq_leq (_sb->rescue_rxt, _tc->snd_congestion))
 
 /**
- * Do fast retransmit with SACKs
+ * Do retransmit with SACKs
  */
-int
-tcp_fast_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-			  u32 burst_size)
+static int
+tcp_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
+		     u32 burst_size)
 {
-  u32 n_written = 0, offset, max_bytes, n_segs = 0, n_segs_now;
+  u32 n_written = 0, offset, max_bytes, n_segs = 0;
   sack_scoreboard_hole_t *hole;
   vlib_main_t *vm = wrk->vm;
   vlib_buffer_t *b = 0;
@@ -1778,12 +1812,19 @@ tcp_fast_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
   int snd_space;
   u8 snd_limited = 0, can_rescue = 0;
 
-  ASSERT (tcp_in_fastrecovery (tc));
+  ASSERT (tcp_in_cong_recovery (tc));
+
+  if (tcp_in_recovery (tc))
+    snd_space = tcp_available_cc_snd_space (tc);
+  else
+    snd_space = tcp_fastrecovery_prr_snd_space (tc);
 
-  snd_space = tcp_available_cc_snd_space (tc);
   if (snd_space < tc->snd_mss)
     {
-      tcp_program_fastretransmit (tc);
+      /* We're cc constrained so don't accumulate tokens */
+      transport_connection_tx_pacer_reset_bucket (&tc->connection,
+						  vm->
+						  clib_time.last_cpu_time);
       return 0;
     }
 
@@ -1800,19 +1841,26 @@ tcp_fast_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
 				       &snd_limited);
       if (!hole)
 	{
+	  /* We are out of lost holes to retransmit so send some new data. */
 	  if (max_deq)
 	    {
+	      u32 n_segs_new, av_window;
+	      av_window = tc->snd_wnd - (tc->snd_nxt - tc->snd_una);
+	      snd_space = clib_min (snd_space, av_window);
 	      snd_space = clib_min (max_deq, snd_space);
 	      burst_size = clib_min (burst_size - n_segs,
 				     snd_space / tc->snd_mss);
-	      n_segs_now = tcp_fast_retransmit_unsent (wrk, tc, burst_size);
-	      if (max_deq > n_segs_now * tc->snd_mss)
-		tcp_program_fastretransmit (tc);
-	      n_segs += n_segs_now;
+	      burst_size = clib_min (burst_size, TCP_RXT_MAX_BURST);
+	      n_segs_new = tcp_transmit_unsent (wrk, tc, burst_size);
+	      if (max_deq > n_segs_new * tc->snd_mss)
+		tcp_program_retransmit (tc);
+
+	      n_segs += n_segs_new;
 	      goto done;
 	    }
 
-	  if (!can_rescue || scoreboard_rescue_rxt_valid (sb, tc))
+	  if (tcp_in_recovery (tc) || !can_rescue
+	      || scoreboard_rescue_rxt_valid (sb, tc))
 	    break;
 
 	  /* If rescue rxt undefined or less than snd_una then one segment of
@@ -1859,18 +1907,19 @@ tcp_fast_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
     }
 
   if (hole)
-    tcp_program_fastretransmit (tc);
+    tcp_program_retransmit (tc);
 
 done:
+
   return n_segs;
 }
 
 /**
  * Fast retransmit without SACK info
  */
-int
-tcp_fast_retransmit_no_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-			     u32 burst_size)
+static int
+tcp_retransmit_no_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
+			u32 burst_size)
 {
   u32 n_written = 0, offset = 0, bi, max_deq, n_segs_now;
   vlib_main_t *vm = wrk->vm;
@@ -1918,9 +1967,9 @@ send_unsent:
     {
       snd_space = clib_min (max_deq, snd_space);
       burst_size = clib_min (burst_size - n_segs, snd_space / tc->snd_mss);
-      n_segs_now = tcp_fast_retransmit_unsent (wrk, tc, burst_size);
+      n_segs_now = tcp_transmit_unsent (wrk, tc, burst_size);
       if (max_deq > n_segs_now * tc->snd_mss)
-	tcp_program_fastretransmit (tc);
+	tcp_program_retransmit (tc);
       n_segs += n_segs_now;
     }
 
@@ -1932,14 +1981,13 @@ done:
 /**
  * Do fast retransmit
  */
-int
-tcp_fast_retransmit (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-		     u32 burst_size)
+static int
+tcp_retransmit (tcp_worker_ctx_t * wrk, tcp_connection_t * tc, u32 burst_size)
 {
   if (tcp_opts_sack_permitted (&tc->rcv_opts))
-    return tcp_fast_retransmit_sack (wrk, tc, burst_size);
+    return tcp_retransmit_sack (wrk, tc, burst_size);
   else
-    return tcp_fast_retransmit_no_sack (wrk, tc, burst_size);
+    return tcp_retransmit_no_sack (wrk, tc, burst_size);
 }
 
 static int
@@ -1991,7 +2039,7 @@ tcp_send_acks (tcp_connection_t * tc, u32 max_burst_size)
 }
 
 static int
-tcp_do_fastretransmit (tcp_connection_t * tc, u32 max_burst_size)
+tcp_do_retransmit (tcp_connection_t * tc, u32 max_burst_size)
 {
   u32 n_segs = 0, burst_size, sent_bytes, burst_bytes;
   tcp_worker_ctx_t *wrk;
@@ -2003,11 +2051,11 @@ tcp_do_fastretransmit (tcp_connection_t * tc, u32 max_burst_size)
   burst_size = clib_min (max_burst_size, burst_bytes / tc->snd_mss);
   if (!burst_size)
     {
-      tcp_program_fastretransmit (tc);
+      tcp_program_retransmit (tc);
       return 0;
     }
 
-  n_segs = tcp_fast_retransmit (wrk, tc, burst_size);
+  n_segs = tcp_retransmit (wrk, tc, burst_size);
   sent_bytes = clib_min (n_segs * tc->snd_mss, burst_bytes);
   transport_connection_tx_pacer_update_bytes (&tc->connection, sent_bytes);
   return n_segs;
@@ -2019,10 +2067,10 @@ tcp_session_custom_tx (void *conn, u32 max_burst_size)
   tcp_connection_t *tc = (tcp_connection_t *) conn;
   u32 n_segs = 0;
 
-  if (tcp_in_fastrecovery (tc) && (tc->flags & TCP_CONN_FRXT_PENDING))
+  if (tcp_in_cong_recovery (tc) && (tc->flags & TCP_CONN_RXT_PENDING))
     {
-      tc->flags &= ~TCP_CONN_FRXT_PENDING;
-      n_segs = tcp_do_fastretransmit (tc, max_burst_size);
+      tc->flags &= ~TCP_CONN_RXT_PENDING;
+      n_segs = tcp_do_retransmit (tc, max_burst_size);
       max_burst_size -= n_segs;
     }
 
diff --git a/src/vnet/tcp/tcp_packet.h b/src/vnet/tcp/tcp_packet.h
index 18b70ebb1ad..1e637a83271 100644
--- a/src/vnet/tcp/tcp_packet.h
+++ b/src/vnet/tcp/tcp_packet.h
@@ -143,9 +143,8 @@ typedef struct _sack_block
 typedef struct
 {
   u8 flags;		/** Option flags, see above */
-
-  u16 mss;		/**< Maximum segment size advertised */
   u8 wscale;		/**< Window scale advertised */
+  u16 mss;		/**< Maximum segment size advertised */
   u32 tsval;		/**< Timestamp value */
   u32 tsecr;		/**< Echoed/reflected time stamp */
   sack_block_t *sacks;	/**< SACK blocks */