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, 61 insertions, 0 deletions

diff --git a/src/vnet/session/transport_interface.h b/src/vnet/session/transport_interface.h
index 745a7db444c..ec9bd43e30f 100644
--- a/src/vnet/session/transport_interface.h
+++ b/src/vnet/session/transport_interface.h
@@ -102,6 +102,67 @@ transport_tx_fn_type_t transport_protocol_tx_fn_type (transport_proto_t tp);
 void transport_update_time (f64 time_now, u8 thread_index);
 void transport_enable_disable (vlib_main_t * vm, u8 is_en);
 
+/**
+ * Initialize tx pacer for connection
+ *
+ * @param tc				transport connection
+ * @param rate_bytes_per_second		initial byte rate
+ * @param burst_bytes			initial burst size in bytes
+ */
+void transport_connection_tx_pacer_init (transport_connection_t * tc,
+					 u32 rate_bytes_per_sec,
+					 u32 burst_bytes);
+
+/**
+ * Update tx pacer pacing rate
+ *
+ * @param tc			transport connection
+ * @param bytes_per_sec		new pacing rate
+ */
+void transport_connection_tx_pacer_update (transport_connection_t * tc,
+					   u64 bytes_per_sec);
+
+/**
+ * Get maximum tx burst allowed for transport connection
+ *
+ * @param tc		transport connection
+ * @param time_now	current cpu time as returned by @ref clib_cpu_time_now
+ */
+u32 transport_connection_max_tx_burst (transport_connection_t * tc,
+				       u64 time_now);
+
+/**
+ * Initialize period for tx pacers
+ *
+ * Defines a unit of time with respect to number of cpu cycles that is to
+ * be used by all tx pacers.
+ */
+void transport_init_tx_pacers_period (void);
+
+/**
+ * Check if transport connection is paced
+ */
+always_inline u8
+transport_connection_is_tx_paced (transport_connection_t * tc)
+{
+  return (tc->flags & TRANSPORT_CONNECTION_F_IS_TX_PACED);
+}
+
+u8 *format_transport_pacer (u8 * s, va_list * args);
+
+/**
+ * Update tx byte stats for transport connection
+ *
+ * If tx pacing is enabled, this also updates pacer bucket to account for the
+ * amount of bytes that have been sent.
+ *
+ * @param tc		transport connection
+ * @param pkts		packets recently sent
+ * @param bytes		bytes recently sent
+ */
+void transport_connection_update_tx_stats (transport_connection_t * tc,
+					   u32 bytes);
+
 #endif /* SRC_VNET_SESSION_TRANSPORT_INTERFACE_H_ */
 
 /*