session: reschedule asap when snd space constrained

Type: feature

Improves fairness for sessions that are snd space or pacer constrained.

Change-Id: Ida5f523090f1dcbfb17bf5116bc7917747ac8593
Signed-off-by: Florin Coras <fcoras@cisco.com>
(cherry picked from commit dd97a48d9fac91c7f16a31aa661dd6c968c3b760)

2 files changed, 28 insertions, 7 deletions

diff --git a/src/vnet/session/session.h b/src/vnet/session/session.h
index f738f3957e2..9fe35b19b25 100644
--- a/src/vnet/session/session.h
+++ b/src/vnet/session/session.h
@@ -221,6 +221,14 @@ session_evt_add_old (session_worker_t * wrk, session_evt_elt_t * elt)
 		       pool_elt_at_index (wrk->event_elts, wrk->old_head));
 }
 
+static inline void
+session_evt_add_head_old (session_worker_t * wrk, session_evt_elt_t * elt)
+{
+  clib_llist_add (wrk->event_elts, evt_list, elt,
+		  pool_elt_at_index (wrk->event_elts, wrk->old_head));
+}
+
+
 static inline u32
 session_evt_ctrl_data_alloc (session_worker_t * wrk)
 {
diff --git a/src/vnet/session/session_node.c b/src/vnet/session/session_node.c
index d4470e0b283..1ace416c802 100644
--- a/src/vnet/session/session_node.c
+++ b/src/vnet/session/session_node.c
@@ -865,14 +865,22 @@ session_tx_fifo_read_and_snd_i (session_worker_t * wrk,
     }
 
   ctx->snd_mss = ctx->transport_vft->send_mss (ctx->tc);
+  if (PREDICT_FALSE (ctx->snd_mss == 0))
+    {
+      session_evt_add_old (wrk, elt);
+      return SESSION_TX_NO_DATA;
+    }
+
   ctx->snd_space = transport_connection_snd_space (ctx->tc,
 						   vm->clib_time.
 						   last_cpu_time,
 						   ctx->snd_mss);
 
-  if (ctx->snd_space == 0 || ctx->snd_mss == 0)
+  /* This flow queue is "empty" so it should be re-evaluated before
+   * the ones that have data to send. */
+  if (ctx->snd_space == 0)
     {
-      session_evt_add_old (wrk, elt);
+      session_evt_add_head_old (wrk, elt);
       return SESSION_TX_NO_DATA;
     }
 
@@ -898,7 +906,7 @@ session_tx_fifo_read_and_snd_i (session_worker_t * wrk,
     {
       if (n_bufs)
 	vlib_buffer_free (vm, wrk->tx_buffers, n_bufs);
-      session_evt_add_old (wrk, elt);
+      session_evt_add_head_old (wrk, elt);
       vlib_node_increment_counter (wrk->vm, node->node_index,
 				   SESSION_QUEUE_ERROR_NO_BUFFER, 1);
       return SESSION_TX_NO_BUFFERS;
@@ -1334,19 +1342,24 @@ session_queue_node_fn (vlib_main_t * vm, vlib_node_runtime_t * node,
 
   if (old_ti != wrk->old_head)
     {
+      clib_llist_index_t ei, next_ei;
+
       old_he = pool_elt_at_index (wrk->event_elts, wrk->old_head);
+      ei = clib_llist_next_index (old_he, evt_list);
+
       while (n_tx_packets < VLIB_FRAME_SIZE)
 	{
-	  clib_llist_index_t ei;
+	  elt = pool_elt_at_index (wrk->event_elts, ei);
+	  next_ei = clib_llist_next_index (elt, evt_list);
+	  clib_llist_remove (wrk->event_elts, evt_list, elt);
 
-	  clib_llist_pop_first (wrk->event_elts, evt_list, elt, old_he);
-	  ei = clib_llist_entry_index (wrk->event_elts, elt);
 	  session_event_dispatch_io (wrk, node, elt, thread_index,
 				     &n_tx_packets);
 
-	  old_he = pool_elt_at_index (wrk->event_elts, wrk->old_head);
 	  if (ei == old_ti)
 	    break;
+
+	  ei = next_ei;
 	};
     }