tcp: send enough dupacks to cover all sack holes

Make sure we send enough dupacks to cover all the holes created in the
last frame received. Also make sure we send all the blocks, not just the
first.

Change-Id: I9597a34ac14473d1cc3ad07d65bc37043e3d0582
Signed-off-by: Florin Coras <fcoras@cisco.com>

4 files changed, 37 insertions, 14 deletions

diff --git a/src/vnet/tcp/tcp.c b/src/vnet/tcp/tcp.c
index c51224447fc..9f35b82a16f 100644
--- a/src/vnet/tcp/tcp.c
+++ b/src/vnet/tcp/tcp.c
@@ -840,7 +840,7 @@ format_tcp_vars (u8 * s, va_list * args)
 	      tcp_rcv_wnd_available (tc));
   s = format (s, " tsval_recent %u tsval_recent_age %u\n", tc->tsval_recent,
 	      tcp_time_now () - tc->tsval_recent_age);
-  s = format (s, " rto %u rto_boff %u srtt %u us %.3f rttvar %u rtt_ts %x",
+  s = format (s, " rto %u rto_boff %u srtt %u us %.3f rttvar %u rtt_ts %.4f",
 	      tc->rto, tc->rto_boff, tc->srtt, tc->mrtt_us * 1000, tc->rttvar,
 	      tc->rtt_ts);
   s = format (s, " rtt_seq %u\n", tc->rtt_seq - tc->iss);
diff --git a/src/vnet/tcp/tcp.h b/src/vnet/tcp/tcp.h
index d1fbf156ed5..a4e7935dfe4 100644
--- a/src/vnet/tcp/tcp.h
+++ b/src/vnet/tcp/tcp.h
@@ -303,6 +303,7 @@ typedef struct _tcp_connection
   tcp_options_t rcv_opts;	/**< Rx options for connection */
 
   sack_block_t *snd_sacks;	/**< Vector of SACKs to send. XXX Fixed size? */
+  u8 snd_sack_pos;		/**< Position in vec of first block to send */
   sack_scoreboard_t sack_sb;	/**< SACK "scoreboard" that tracks holes */
 
   u16 rcv_dupacks;	/**< Number of DUPACKs received */
diff --git a/src/vnet/tcp/tcp_debug.h b/src/vnet/tcp/tcp_debug.h
index cf074925435..7ef7558637e 100755
--- a/src/vnet/tcp/tcp_debug.h
+++ b/src/vnet/tcp/tcp_debug.h
@@ -20,8 +20,8 @@
 
 #define TCP_DEBUG (1)
 #define TCP_DEBUG_SM (0)
-#define TCP_DEBUG_CC (0)
-#define TCP_DEBUG_CC_STAT (0)
+#define TCP_DEBUG_CC (1)
+#define TCP_DEBUG_CC_STAT (1)
 #define TCP_DEBUG_BUFFER_ALLOCATION (0)
 
 #define foreach_tcp_dbg_evt		\
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;
 }