tcp: track reorder with sacks

Type: feature

Change-Id: I041bff2e8d589c171661de286fa1503531dff891
Signed-off-by: Florin Coras <fcoras@cisco.com>

6 files changed, 61 insertions, 38 deletions

diff --git a/src/vnet/tcp/tcp.c b/src/vnet/tcp/tcp.c
index 938a863238f..1563be4eb86 100644
--- a/src/vnet/tcp/tcp.c
+++ b/src/vnet/tcp/tcp.c
@@ -925,17 +925,21 @@ tcp_snd_space_inline (tcp_connection_t * tc)
    * 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 (PREDICT_FALSE (tc->rcv_dupacks || tc->sack_sb.sacked_bytes))
     {
-      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)))
+      int snt_limited, n_pkts;
+
+      n_pkts = tcp_opts_sack_permitted (&tc->rcv_opts)
+	? tc->sack_sb.reorder - 1 : 2;
+
+      if ((seq_lt (tc->limited_transmit, tc->snd_nxt - n_pkts * 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));
 
-      int snt_limited = tc->snd_nxt - tc->limited_transmit;
-      snd_space = clib_max ((int) 2 * tc->snd_mss - snt_limited, 0);
+      snt_limited = tc->snd_nxt - tc->limited_transmit;
+      snd_space = clib_max (n_pkts * tc->snd_mss - snt_limited, 0);
     }
   return tcp_round_snd_space (tc, snd_space);
 }
diff --git a/src/vnet/tcp/tcp_cli.c b/src/vnet/tcp/tcp_cli.c
index 6ad2425b53d..edd4d2d1bc1 100644
--- a/src/vnet/tcp/tcp_cli.c
+++ b/src/vnet/tcp/tcp_cli.c
@@ -341,9 +341,10 @@ format_tcp_scoreboard (u8 * s, va_list * args)
 	      " rxt_sacked %u\n",
 	      sb->sacked_bytes, sb->last_sacked_bytes, sb->lost_bytes,
 	      sb->last_lost_bytes, sb->rxt_sacked);
-  s = format (s, "%Ulast_delivered %u high_sacked %u is_reneging %u\n",
+  s = format (s, "%Ulast_delivered %u high_sacked %u is_reneging %u",
 	      format_white_space, indent, sb->last_bytes_delivered,
 	      sb->high_sacked - tc->iss, sb->is_reneging);
+  s = format (s, " reorder %u\n", sb->reorder);
   s = format (s, "%Ucur_rxt_hole %u high_rxt %u rescue_rxt %u",
 	      format_white_space, indent, sb->cur_rxt_hole,
 	      sb->high_rxt - tc->iss, sb->rescue_rxt - tc->iss);
diff --git a/src/vnet/tcp/tcp_input.c b/src/vnet/tcp/tcp_input.c
index 5fa7bf23c72..de9d89181fa 100644
--- a/src/vnet/tcp/tcp_input.c
+++ b/src/vnet/tcp/tcp_input.c
@@ -689,7 +689,7 @@ tcp_cc_init_congestion (tcp_connection_t * tc)
    * 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;
+    tc->cwnd += TCP_DUPACK_THRESHOLD * tc->snd_mss;
 
   tc->fr_occurences += 1;
   TCP_EVT (TCP_EVT_CC_EVT, tc, 4);
@@ -721,14 +721,6 @@ 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, u8 has_sack)
 {
   if (!has_sack)
@@ -752,8 +744,7 @@ tcp_should_fastrecover (tcp_connection_t * tc, u8 has_sack)
 	  return 0;
 	}
     }
-  return ((tc->rcv_dupacks == TCP_DUPACK_THRESHOLD)
-	  || tcp_should_fastrecover_sack (tc));
+  return tc->sack_sb.lost_bytes || tc->rcv_dupacks >= tc->sack_sb.reorder;
 }
 
 static int
diff --git a/src/vnet/tcp/tcp_output.c b/src/vnet/tcp/tcp_output.c
index e9bff5b954a..294b18c0294 100644
--- a/src/vnet/tcp/tcp_output.c
+++ b/src/vnet/tcp/tcp_output.c
@@ -1290,6 +1290,7 @@ tcp_cc_init_rxt_timeout (tcp_connection_t * tc)
   tc->rtt_ts = 0;
   tc->cwnd_acc_bytes = 0;
   tc->tr_occurences += 1;
+  tc->sack_sb.reorder = TCP_DUPACK_THRESHOLD;
   tcp_recovery_on (tc);
 }
 
diff --git a/src/vnet/tcp/tcp_sack.c b/src/vnet/tcp/tcp_sack.c
index b9e1166d779..8f51b517361 100644
--- a/src/vnet/tcp/tcp_sack.c
+++ b/src/vnet/tcp/tcp_sack.c
@@ -88,10 +88,23 @@ scoreboard_insert_hole (sack_scoreboard_t * sb, u32 prev_index,
 }
 
 always_inline void
-scoreboard_update_sacked_rxt (sack_scoreboard_t * sb, u32 start, u32 end,
-			      u8 has_rxt)
+scoreboard_update_sacked (sack_scoreboard_t * sb, u32 start, u32 end,
+			  u8 has_rxt, u16 snd_mss)
 {
-  if (!has_rxt || seq_geq (start, sb->high_rxt))
+  if (!has_rxt)
+    {
+      /* Sequence was not retransmitted but it was sacked. Estimate reorder
+       * only if not in congestion recovery */
+      if (seq_lt (start, sb->high_sacked))
+	{
+	  u32 reord = (sb->high_sacked - start + snd_mss - 1) / snd_mss;
+	  reord = clib_min (reord, TCP_MAX_SACK_REORDER);
+	  sb->reorder = clib_max (sb->reorder, reord);
+	}
+      return;
+    }
+
+  if (seq_geq (start, sb->high_rxt))
     return;
 
   sb->rxt_sacked +=
@@ -125,8 +138,14 @@ scoreboard_update_bytes (sack_scoreboard_t * sb, u32 ack, u32 snd_mss)
       blks = 1;
     }
 
-  while (sacked < (TCP_DUPACK_THRESHOLD - 1) * snd_mss
-	 && blks < TCP_DUPACK_THRESHOLD)
+  /* As per RFC 6675 a sequence number is lost if:
+   *   DupThresh discontiguous SACKed sequences have arrived above
+   *   'SeqNum' or more than (DupThresh - 1) * SMSS bytes with sequence
+   *   numbers greater than 'SeqNum' have been SACKed.
+   * To avoid spurious retransmits, use reordering estimate instead of
+   * DupThresh to detect loss.
+   */
+  while (sacked <= (sb->reorder - 1) * snd_mss && blks < sb->reorder)
     {
       if (right->is_lost)
 	sb->lost_bytes += scoreboard_hole_bytes (right);
@@ -251,6 +270,7 @@ scoreboard_init (sack_scoreboard_t * sb)
   sb->head = TCP_INVALID_SACK_HOLE_INDEX;
   sb->tail = TCP_INVALID_SACK_HOLE_INDEX;
   sb->cur_rxt_hole = TCP_INVALID_SACK_HOLE_INDEX;
+  sb->reorder = TCP_DUPACK_THRESHOLD;
 }
 
 void
@@ -270,6 +290,7 @@ scoreboard_clear (sack_scoreboard_t * sb)
   sb->last_lost_bytes = 0;
   sb->cur_rxt_hole = TCP_INVALID_SACK_HOLE_INDEX;
   sb->is_reneging = 0;
+  sb->reorder = TCP_DUPACK_THRESHOLD;
 }
 
 void
@@ -307,7 +328,7 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
   sack_scoreboard_hole_t *hole, *next_hole;
   sack_scoreboard_t *sb = &tc->sack_sb;
   sack_block_t *blk, *rcv_sacks;
-  u32 blk_index = 0, i, j;
+  u32 blk_index = 0, i, j, high_sacked;
   u8 has_rxt;
 
   sb->last_sacked_bytes = 0;
@@ -391,8 +412,9 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
 	  hole = scoreboard_insert_hole (sb, TCP_INVALID_SACK_HOLE_INDEX,
 					 tc->snd_una, tc->snd_nxt);
 	  sb->tail = scoreboard_hole_index (sb, hole);
+	  sb->high_sacked = tc->snd_una;
 	}
-      sb->high_sacked = rcv_sacks[vec_len (rcv_sacks) - 1].end;
+      high_sacked = rcv_sacks[vec_len (rcv_sacks) - 1].end;
     }
   else
     {
@@ -412,11 +434,10 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
 				      tc->snd_nxt);
 	    }
 	}
-
       /* Keep track of max byte sacked for when the last hole
        * is acked */
-      sb->high_sacked = seq_max (rcv_sacks[vec_len (rcv_sacks) - 1].end,
-				 sb->high_sacked);
+      high_sacked = seq_max (rcv_sacks[vec_len (rcv_sacks) - 1].end,
+			     sb->high_sacked);
     }
 
   /* Walk the holes with the SACK blocks */
@@ -442,7 +463,8 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
 	      /* If covered by ack, compute delivered bytes */
 	      if (blk->end == ack)
 		{
-		  u32 sacked = next_hole ? next_hole->start : sb->high_sacked;
+		  u32 sacked = next_hole ? next_hole->start :
+		    seq_max (sb->high_sacked, hole->end);
 		  if (PREDICT_FALSE (seq_lt (ack, sacked)))
 		    {
 		      sb->last_bytes_delivered += ack - hole->end;
@@ -454,8 +476,8 @@ 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_update_sacked (sb, hole->start, hole->end,
+					has_rxt, tc->snd_mss);
 	      scoreboard_remove_hole (sb, hole);
 	      hole = next_hole;
 	    }
@@ -464,8 +486,8 @@ 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);
+		  scoreboard_update_sacked (sb, hole->start, blk->end,
+					    has_rxt, tc->snd_mss);
 		  hole->start = blk->end;
 		}
 	      blk_index++;
@@ -482,23 +504,25 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
 	      /* Pool might've moved */
 	      hole = scoreboard_get_hole (sb, hole_index);
 	      hole->end = blk->start;
+	      next_hole->is_lost = hole->is_lost;
 
-	      scoreboard_update_sacked_rxt (sb, blk->start, blk->end,
-					    has_rxt);
+	      scoreboard_update_sacked (sb, blk->start, blk->end,
+					has_rxt, tc->snd_mss);
 
 	      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);
+	      scoreboard_update_sacked (sb, blk->start, hole->end,
+					has_rxt, tc->snd_mss);
 	      hole->end = blk->start;
 	    }
 	  hole = scoreboard_next_hole (sb, hole);
 	}
     }
 
+  sb->high_sacked = high_sacked;
   scoreboard_update_bytes (sb, ack, tc->snd_mss);
 
   ASSERT (sb->last_sacked_bytes <= sb->sacked_bytes || tcp_in_recovery (tc));
diff --git a/src/vnet/tcp/tcp_types.h b/src/vnet/tcp/tcp_types.h
index d7bcac5e3bc..027f0e63300 100644
--- a/src/vnet/tcp/tcp_types.h
+++ b/src/vnet/tcp/tcp_types.h
@@ -151,6 +151,7 @@ typedef enum tcp_connection_flag_
 #define TCP_SCOREBOARD_TRACE (0)
 #define TCP_MAX_SACK_BLOCKS 255	/**< Max number of SACK blocks stored */
 #define TCP_INVALID_SACK_HOLE_INDEX ((u32)~0)
+#define TCP_MAX_SACK_REORDER 300
 
 typedef struct _scoreboard_trace_elt
 {
@@ -185,7 +186,8 @@ typedef struct _sack_scoreboard
   u32 lost_bytes;			/**< Bytes lost as per RFC6675 */
   u32 last_lost_bytes;			/**< Number of bytes last lost */
   u32 cur_rxt_hole;			/**< Retransmitting from this hole */
-  u8 is_reneging;
+  u32 reorder;				/**< Estimate of segment reordering */
+  u8 is_reneging;			/**< Flag set if peer is reneging*/
 
 #if TCP_SCOREBOARD_TRACE
   scoreboard_trace_elt_t *trace;