1 files changed, 33 insertions, 11 deletions

diff --git a/src/vnet/tcp/tcp_output.c b/src/vnet/tcp/tcp_output.c
index 725ffec0852..4de479c344b 100644
--- a/src/vnet/tcp/tcp_output.c
+++ b/src/vnet/tcp/tcp_output.c
@@ -253,14 +253,12 @@ tcp_options_write (u8 * data, tcp_options_t * opts)
   if (tcp_opts_sack (opts))
     {
       int i;
-      u32 n_sack_blocks = clib_min (vec_len (opts->sacks),
-				    TCP_OPTS_MAX_SACK_BLOCKS);
 
-      if (n_sack_blocks != 0)
+      if (opts->n_sack_blocks != 0)
 	{
 	  *data++ = TCP_OPTION_SACK_BLOCK;
-	  *data++ = 2 + n_sack_blocks * TCP_OPTION_LEN_SACK_BLOCK;
-	  for (i = 0; i < n_sack_blocks; i++)
+	  *data++ = 2 + opts->n_sack_blocks * TCP_OPTION_LEN_SACK_BLOCK;
+	  for (i = 0; i < opts->n_sack_blocks; i++)
 	    {
 	      buf = clib_host_to_net_u32 (opts->sacks[i].start);
 	      clib_memcpy_fast (data, &buf, seq_len);
@@ -269,7 +267,7 @@ tcp_options_write (u8 * data, tcp_options_t * opts)
 	      clib_memcpy_fast (data, &buf, seq_len);
 	      data += seq_len;
 	    }
-	  opts_len += 2 + n_sack_blocks * TCP_OPTION_LEN_SACK_BLOCK;
+	  opts_len += 2 + opts->n_sack_blocks * TCP_OPTION_LEN_SACK_BLOCK;
 	}
     }
 
@@ -372,9 +370,13 @@ tcp_make_established_options (tcp_connection_t * tc, tcp_options_t * opts)
       if (vec_len (tc->snd_sacks))
 	{
 	  opts->flags |= TCP_OPTS_FLAG_SACK;
-	  opts->sacks = tc->snd_sacks;
-	  opts->n_sack_blocks = clib_min (vec_len (tc->snd_sacks),
+	  if (tc->snd_sack_pos >= vec_len (tc->snd_sacks))
+	    tc->snd_sack_pos = 0;
+	  opts->sacks = &tc->snd_sacks[tc->snd_sack_pos];
+	  opts->n_sack_blocks = vec_len (tc->snd_sacks) - tc->snd_sack_pos;
+	  opts->n_sack_blocks = clib_min (opts->n_sack_blocks,
 					  TCP_OPTS_MAX_SACK_BLOCKS);
+	  tc->snd_sack_pos += opts->n_sack_blocks;
 	  len += 2 + TCP_OPTION_LEN_SACK_BLOCK * opts->n_sack_blocks;
 	}
     }
@@ -1250,14 +1252,34 @@ tcp_send_acks (tcp_worker_ctx_t * wrk)
     {
       tc = tcp_connection_get (pending_acks[i], thread_index);
       tc->flags &= ~TCP_CONN_SNDACK;
-      n_acks = clib_max (1, tc->pending_dupacks);
+      if (!tc->pending_dupacks)
+	{
+	  tcp_send_ack (tc);
+	  continue;
+	}
+
       /* If we're supposed to send dupacks but have no ooo data
        * send only one ack */
-      if (tc->pending_dupacks && !vec_len (tc->snd_sacks))
-	n_acks = 1;
+      if (!vec_len (tc->snd_sacks))
+	{
+	  tcp_send_ack (tc);
+	  continue;
+	}
+
+      /* Start with first sack block */
+      tc->snd_sack_pos = 0;
+
+      /* Generate enough dupacks to cover all sack blocks. Do not generate
+       * more sacks than the number of packets received. But do generate at
+       * least 3, i.e., the number needed to signal congestion, if needed. */
+      n_acks = vec_len (tc->snd_sacks) / TCP_OPTS_MAX_SACK_BLOCKS;
+      n_acks = clib_min (n_acks, tc->pending_dupacks);
+      n_acks = clib_max (n_acks, clib_min (tc->pending_dupacks, 3));
       for (j = 0; j < n_acks; j++)
 	tcp_send_ack (tc);
+
       tc->pending_dupacks = 0;
+      tc->snd_sack_pos = 0;
     }
   _vec_len (wrk->pending_acks) = 0;
 }