tcp: use sacks for timer based recovery

Type: feature

If available, reuse sack scoreboard in timer triggered retransmit to
minimize spurious retransmits.

Additional changes/refactoring:
- limited transmit updates
- add sacked rxt count to scoreboard
- prr pacing of fast retransmits
- startup pacing updates
- changed loss window to flight + mss

Change-Id: I057de6a9d6401698bd1031d5cf5cfbb62f2bdf61
Signed-off-by: Florin Coras <fcoras@cisco.com>
(cherry picked from commit 36ebcfffbc7ab0e83b4bb8dfaec16bf16cafb954)

1 files changed, 25 insertions, 27 deletions

diff --git a/src/vnet/tcp/tcp.h b/src/vnet/tcp/tcp.h
index 227b3f8a856..a1b7d4cbd0d 100644
--- a/src/vnet/tcp/tcp.h
+++ b/src/vnet/tcp/tcp.h
@@ -32,6 +32,7 @@
 #define TCP_MAX_OPTION_SPACE 40
 #define TCP_CC_DATA_SZ 24
 #define TCP_MAX_GSO_SZ 65536
+#define TCP_RXT_MAX_BURST 10
 
 #define TCP_DUPACK_THRESHOLD 	3
 #define TCP_IW_N_SEGMENTS 	10
@@ -111,7 +112,7 @@ extern timer_expiration_handler tcp_timer_retransmit_syn_handler;
   _(DCNT_PENDING, "Disconnect pending")		\
   _(HALF_OPEN_DONE, "Half-open completed")	\
   _(FINPNDG, "FIN pending")			\
-  _(FRXT_PENDING, "Fast-retransmit pending")	\
+  _(RXT_PENDING, "Retransmit pending")		\
   _(FRXT_FIRST, "Fast-retransmit first again")	\
   _(DEQ_PENDING, "Pending dequeue acked")	\
   _(PSH_PENDING, "PSH pending")			\
@@ -166,6 +167,7 @@ typedef struct _sack_scoreboard
   u32 sacked_bytes;			/**< Number of bytes sacked in sb */
   u32 last_sacked_bytes;		/**< Number of bytes last sacked */
   u32 last_bytes_delivered;		/**< Sack bytes delivered to app */
+  u32 rxt_sacked;			/**< Rxt last delivered */
   u32 high_sacked;			/**< Highest byte sacked (fack) */
   u32 high_rxt;				/**< Highest retransmitted sequence */
   u32 rescue_rxt;			/**< Rescue sequence number */
@@ -219,8 +221,11 @@ sack_scoreboard_hole_t *scoreboard_prev_hole (sack_scoreboard_t * sb,
 					      sack_scoreboard_hole_t * hole);
 sack_scoreboard_hole_t *scoreboard_first_hole (sack_scoreboard_t * sb);
 sack_scoreboard_hole_t *scoreboard_last_hole (sack_scoreboard_t * sb);
+
 void scoreboard_clear (sack_scoreboard_t * sb);
+void scoreboard_clear_reneging (sack_scoreboard_t * sb, u32 start, u32 end);
 void scoreboard_init (sack_scoreboard_t * sb);
+void scoreboard_init_high_rxt (sack_scoreboard_t * sb, u32 snd_una);
 u8 *format_tcp_scoreboard (u8 * s, va_list * args);
 
 #define TCP_BTS_INVALID_INDEX	((u32)~0)
@@ -360,8 +365,10 @@ typedef struct _tcp_connection
   u32 prev_cwnd;	/**< ssthresh before congestion */
   u32 bytes_acked;	/**< Bytes acknowledged by current segment */
   u32 burst_acked;	/**< Bytes acknowledged in current burst */
-  u32 snd_rxt_bytes;	/**< Retransmitted bytes */
+  u32 snd_rxt_bytes;	/**< Retransmitted bytes during current cc event */
   u32 snd_rxt_ts;	/**< Timestamp when first packet is retransmitted */
+  u32 prr_delivered;	/**< RFC6937 bytes delivered during current event */
+  u32 rxt_delivered;	/**< Rxt bytes delivered during current cc event */
   u32 tsecr_last_ack;	/**< Timestamp echoed to us in last healthy ACK */
   u32 snd_congestion;	/**< snd_una_max when congestion is detected */
   u32 tx_fifo_size;	/**< Tx fifo size. Used to constrain cwnd */
@@ -757,7 +764,7 @@ void tcp_send_window_update_ack (tcp_connection_t * tc);
 
 void tcp_program_ack (tcp_connection_t * tc);
 void tcp_program_dupack (tcp_connection_t * tc);
-void tcp_program_fastretransmit (tcp_connection_t * tc);
+void tcp_program_retransmit (tcp_connection_t * tc);
 
 /*
  * Rate estimation
@@ -857,18 +864,9 @@ tcp_flight_size (const tcp_connection_t * tc)
   int flight_size;
 
   flight_size = (int) (tc->snd_nxt - tc->snd_una) - tcp_bytes_out (tc)
-    + tc->snd_rxt_bytes;
+    + tc->snd_rxt_bytes - tc->rxt_delivered;
 
-  if (flight_size < 0)
-    {
-      if (0)
-	clib_warning
-	  ("Negative: %u %u %u dupacks %u sacked bytes %u flags %d",
-	   tc->snd_una_max - tc->snd_una, tcp_bytes_out (tc),
-	   tc->snd_rxt_bytes, tc->rcv_dupacks, tc->sack_sb.sacked_bytes,
-	   tc->rcv_opts.flags);
-      return 0;
-    }
+  ASSERT (flight_size >= 0);
 
   return flight_size;
 }
@@ -912,7 +910,8 @@ tcp_cwnd_accumulate (tcp_connection_t * tc, u32 thresh, u32 bytes)
 always_inline u32
 tcp_loss_wnd (const tcp_connection_t * tc)
 {
-  return tc->snd_mss;
+  /* Whatever we have in flight + the packet we're about to send */
+  return tcp_flight_size (tc) + tc->snd_mss;
 }
 
 always_inline u32
@@ -951,22 +950,14 @@ tcp_available_cc_snd_space (const tcp_connection_t * tc)
 always_inline u8
 tcp_is_lost_fin (tcp_connection_t * tc)
 {
-  if ((tc->flags & TCP_CONN_FINSNT) && tc->snd_una_max - tc->snd_una == 1)
+  if ((tc->flags & TCP_CONN_FINSNT) && (tc->snd_una_max - tc->snd_una == 1))
     return 1;
   return 0;
 }
 
 u32 tcp_snd_space (tcp_connection_t * tc);
-int tcp_retransmit_first_unacked (tcp_worker_ctx_t * wrk,
-				  tcp_connection_t * tc);
-int tcp_fast_retransmit_no_sack (tcp_worker_ctx_t * wrk,
-				 tcp_connection_t * tc, u32 burst_size);
-int tcp_fast_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-			      u32 burst_size);
-int tcp_fast_retransmit (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
-			 u32 burst_size);
-void tcp_cc_init_congestion (tcp_connection_t * tc);
-void tcp_cc_fastrecovery_clear (tcp_connection_t * tc);
+//void tcp_cc_init_congestion (tcp_connection_t * tc);
+//void tcp_cc_fastrecovery_clear (tcp_connection_t * tc);
 
 fib_node_index_t tcp_lookup_rmt_in_fib (tcp_connection_t * tc);
 
@@ -1036,6 +1027,12 @@ tcp_cc_rcv_cong_ack (tcp_connection_t * tc, tcp_cc_ack_t ack_type,
 }
 
 static inline void
+tcp_cc_congestion (tcp_connection_t * tc)
+{
+  tc->cc_algo->congestion (tc);
+}
+
+static inline void
 tcp_cc_loss (tcp_connection_t * tc)
 {
   tc->cc_algo->loss (tc);
@@ -1068,9 +1065,10 @@ tcp_cc_get_pacing_rate (tcp_connection_t * tc)
     return tc->cc_algo->get_pacing_rate (tc);
 
   f64 srtt = clib_min ((f64) tc->srtt * TCP_TICK, tc->mrtt_us);
+
   /* TODO should constrain to interface's max throughput but
    * we don't have link speeds for sw ifs ..*/
-  return (tc->cwnd / srtt);
+  return ((f64) tc->cwnd / srtt);
 }
 
 always_inline void