tcp/session: add tx pacer

Adds tx pacing infrastructure for transport protocols that want to use
it. Particularly useful for connections with non-negligible rtt and
constrained network throughput as it avoids large tx bursts that lead to
local interface tx or network drops.

By default the pacer is disabled. To enabled it for tcp, add tx-pacing
to tcp's startup conf. We are still slightly inefficient in the handling
of incoming packets in established state so the pacer slightly affect
maximum throughput in low lacency scenarios.

Change-Id: Id445b2ffcd64cce015f75b773f7d722faa0f7ca9
Signed-off-by: Florin Coras <fcoras@cisco.com>

1 files changed, 39 insertions, 5 deletions

diff --git a/src/vnet/tcp/tcp.c b/src/vnet/tcp/tcp.c
index cb05b8c0533..626b49997ac 100644
--- a/src/vnet/tcp/tcp.c
+++ b/src/vnet/tcp/tcp.c
@@ -555,6 +555,16 @@ tcp_init_snd_vars (tcp_connection_t * tc)
   tc->snd_una_max = tc->snd_nxt;
 }
 
+void
+tcp_enable_pacing (tcp_connection_t * tc)
+{
+  u32 max_burst, byte_rate;
+  max_burst = 16 * tc->snd_mss;
+  byte_rate = 2 << 16;
+  transport_connection_tx_pacer_init (&tc->connection, byte_rate, max_burst);
+  tc->mrtt_us = (u32) ~ 0;
+}
+
 /** Initialize tcp connection variables
  *
  * Should be called after having received a msg from the peer, i.e., a SYN or
@@ -572,7 +582,11 @@ tcp_connection_init_vars (tcp_connection_t * tc)
   if (!tc->c_is_ip4 && ip6_address_is_link_local_unicast (&tc->c_rmt_ip6))
     tcp_add_del_adjacency (tc, 1);
 
-  //  tcp_connection_fib_attach (tc);
+  /*  tcp_connection_fib_attach (tc); */
+
+  if (transport_connection_is_tx_paced (&tc->connection)
+      || tcp_main.tx_pacing)
+    tcp_enable_pacing (tc);
 }
 
 static int
@@ -784,14 +798,19 @@ format_tcp_vars (u8 * s, va_list * args)
   s = format (s, " limited_transmit %u\n", tc->limited_transmit - tc->iss);
   s = format (s, " tsecr %u tsecr_last_ack %u\n", tc->rcv_opts.tsecr,
 	      tc->tsecr_last_ack);
-  s = format (s, " rto %u rto_boff %u srtt %u rttvar %u rtt_ts %u ", tc->rto,
-	      tc->rto_boff, tc->srtt, tc->rttvar, tc->rtt_ts);
+  s = format (s, " rto %u rto_boff %u srtt %u rttvar %u rtt_ts %2.5f ",
+	      tc->rto, tc->rto_boff, tc->srtt, tc->rttvar, tc->rtt_ts);
   s = format (s, "rtt_seq %u\n", tc->rtt_seq);
   s = format (s, " tsval_recent %u tsval_recent_age %u\n", tc->tsval_recent,
 	      tcp_time_now () - tc->tsval_recent_age);
   if (tc->state >= TCP_STATE_ESTABLISHED)
-    s = format (s, " scoreboard: %U\n", format_tcp_scoreboard, &tc->sack_sb,
-		tc);
+    {
+      s = format (s, " scoreboard: %U\n", format_tcp_scoreboard, &tc->sack_sb,
+		  tc);
+      if (transport_connection_is_tx_paced (&tc->connection))
+	s = format (s, " pacer: %U\n", format_transport_pacer,
+		    &tc->connection.pacer);
+    }
   if (vec_len (tc->snd_sacks))
     s = format (s, " sacks tx: %U\n", format_tcp_sacks, tc);
 
@@ -1129,6 +1148,19 @@ const static transport_proto_vft_t tcp_proto = {
 };
 /* *INDENT-ON* */
 
+void
+tcp_update_pacer (tcp_connection_t * tc)
+{
+  f64 srtt;
+
+  if (!transport_connection_is_tx_paced (&tc->connection))
+    return;
+
+  srtt = clib_min ((f64) tc->srtt * TCP_TICK, tc->mrtt_us);
+  transport_connection_tx_pacer_update (&tc->connection,
+					((f64) tc->cwnd) / srtt);
+}
+
 static void
 tcp_timer_keep_handler (u32 conn_index)
 {
@@ -1408,6 +1440,8 @@ tcp_config_fn (vlib_main_t * vm, unformat_input_t * input)
       else if (unformat (input, "max-rx-fifo %U", unformat_memory_size,
 			 &tm->max_rx_fifo))
 	;
+      else if (unformat (input, "tx-pacing"))
+	tm->tx_pacing = 1;
       else
 	return clib_error_return (0, "unknown input `%U'",
 				  format_unformat_error, input);