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, 18 insertions, 0 deletions

diff --git a/src/vnet/session/session.h b/src/vnet/session/session.h
index 914e0581fec..f0aa36cc1bc 100644
--- a/src/vnet/session/session.h
+++ b/src/vnet/session/session.h
@@ -215,6 +215,12 @@ struct _session_manager_main
   /** per-worker session context */
   session_tx_context_t *ctx;
 
+  /** Our approximation of a "complete" dispatch loop period */
+  f64 *dispatch_period;
+
+  /** vlib_time_now last time around the track */
+  f64 *last_vlib_time;
+
   /** vpp fifo event queue */
   svm_msg_q_t **vpp_event_queues;
 
@@ -494,6 +500,18 @@ transport_tx_fifo_size (transport_connection_t * tc)
   return s->server_tx_fifo->nitems;
 }
 
+always_inline f64
+transport_dispatch_period (u32 thread_index)
+{
+  return session_manager_main.dispatch_period[thread_index];
+}
+
+always_inline f64
+transport_time_now (u32 thread_index)
+{
+  return session_manager_main.last_vlib_time[thread_index];
+}
+
 always_inline u32
 session_get_index (stream_session_t * s)
 {