Fix TCP loss recovery, VPP-745

Allows pure loss recovery retransmits only on timeout.

Change-Id: I563cdbf9e7b890a6569350bdbda4f746ace0544e
Signed-off-by: Florin Coras <fcoras@cisco.com>

1 files changed, 17 insertions, 27 deletions

diff --git a/src/vnet/tcp/tcp_output.c b/src/vnet/tcp/tcp_output.c
index a85d30daddb..7ee930c61af 100644
--- a/src/vnet/tcp/tcp_output.c
+++ b/src/vnet/tcp/tcp_output.c
@@ -73,7 +73,7 @@ tcp_set_snd_mss (tcp_connection_t * tc)
   snd_mss = dummy_mtu;
 
   /* TODO cache mss and consider PMTU discovery */
-  snd_mss = tc->opt.mss < snd_mss ? tc->opt.mss : snd_mss;
+  snd_mss = clib_min (tc->opt.mss, snd_mss);
 
   tc->snd_mss = snd_mss;
 
@@ -923,6 +923,12 @@ tcp_push_hdr_i (tcp_connection_t * tc, vlib_buffer_t * b,
   /* TODO this is updated in output as well ... */
   if (tc->snd_nxt > tc->snd_una_max)
     tc->snd_una_max = tc->snd_nxt;
+
+  if (tc->rtt_ts == 0)
+    {
+      tc->rtt_ts = tcp_time_now ();
+      tc->rtt_seq = tc->snd_nxt;
+    }
   TCP_EVT_DBG (TCP_EVT_PKTIZE, tc);
 }
 
@@ -1019,9 +1025,10 @@ tcp_rtx_timeout_cc (tcp_connection_t * tc)
     }
 
   /* Start again from the beginning */
-  tcp_recovery_on (tc);
+
   tc->cwnd = tcp_loss_wnd (tc);
   tc->snd_congestion = tc->snd_una_max;
+  tcp_recovery_on (tc);
 }
 
 static void
@@ -1032,7 +1039,7 @@ tcp_timer_retransmit_handler_i (u32 index, u8 is_syn)
   u32 thread_index = vlib_get_thread_index ();
   tcp_connection_t *tc;
   vlib_buffer_t *b;
-  u32 bi, snd_space, n_bytes;
+  u32 bi, n_bytes;
 
   if (is_syn)
     {
@@ -1065,33 +1072,16 @@ tcp_timer_retransmit_handler_i (u32 index, u8 is_syn)
       /* Exponential backoff */
       tc->rto = clib_min (tc->rto << 1, TCP_RTO_MAX);
 
-      /* Figure out what and how many bytes we can send */
-      snd_space = tcp_available_snd_space (tc);
-
       TCP_EVT_DBG (TCP_EVT_CC_EVT, tc, 1);
 
-      if (snd_space == 0)
-	{
-	  clib_warning ("no wnd to retransmit");
-	  tcp_return_buffer (tm);
-
-	  /* Force one segment */
-	  tcp_retransmit_first_unacked (tc);
+      /* Send one segment. No fancy recovery for now! */
+      n_bytes = tcp_prepare_retransmit_segment (tc, b, 0, tc->snd_mss);
+      scoreboard_clear (&tc->sack_sb);
 
-	  /* Re-enable retransmit timer. Output may be unwilling
-	   * to do it for us */
-	  tcp_retransmit_timer_set (tc);
-
-	  return;
-	}
-      else
+      if (n_bytes == 0)
 	{
-	  /* No fancy recovery for now! */
-	  n_bytes = tcp_prepare_retransmit_segment (tc, b, 0, snd_space);
-	  scoreboard_clear (&tc->sack_sb);
-
-	  if (n_bytes == 0)
-	    return;
+	  clib_warning ("could not retransmit");
+	  return;
 	}
     }
   else
@@ -1400,7 +1390,7 @@ tcp46_output_inline (vlib_main_t * vm,
 	    }
 
 	  /* If not retransmitting
-	   * 1) update snd_una_max (SYN, SYNACK, new data, FIN)
+	   * 1) update snd_una_max (SYN, SYNACK, FIN)
 	   * 2) If we're not tracking an ACK, start tracking */
 	  if (seq_lt (tc0->snd_una_max, tc0->snd_nxt))
 	    {