session tcp udp: consolidate transport snd apis

Type: improvement

Use only one api to retrieve transport send parameters. Additionally,
allow transports to request postponing and descheduling of events.

With this, tcp now requests descheduling of sessions when the
connections are stuck probing for zero snd_wnd

Signed-off-by: Florin Coras <fcoras@cisco.com>
Change-Id: I722c974f3e68fa15424c519a1fffacda43af050c

1 files changed, 39 insertions, 37 deletions

diff --git a/src/vnet/session/session_node.c b/src/vnet/session/session_node.c
index ad24f429fbc..b1c2428874e 100644
--- a/src/vnet/session/session_node.c
+++ b/src/vnet/session/session_node.c
@@ -567,7 +567,7 @@ session_tx_fifo_chain_tail (vlib_main_t * vm, session_tx_context_t * ctx,
   b->total_length_not_including_first_buffer = 0;
 
   chain_b = b;
-  left_from_seg = clib_min (ctx->snd_mss - b->current_length,
+  left_from_seg = clib_min (ctx->sp.snd_mss - b->current_length,
 			    ctx->left_to_snd);
   to_deq = left_from_seg;
   for (j = 1; j < ctx->n_bufs_per_seg; j++)
@@ -583,8 +583,8 @@ session_tx_fifo_chain_tail (vlib_main_t * vm, session_tx_context_t * ctx,
       if (peek_data)
 	{
 	  n_bytes_read = svm_fifo_peek (ctx->s->tx_fifo,
-					ctx->tx_offset, len_to_deq, data);
-	  ctx->tx_offset += n_bytes_read;
+					ctx->sp.tx_offset, len_to_deq, data);
+	  ctx->sp.tx_offset += n_bytes_read;
 	}
       else
 	{
@@ -651,12 +651,12 @@ session_tx_fill_buffer (vlib_main_t * vm, session_tx_context_t * ctx,
 
   if (peek_data)
     {
-      n_bytes_read = svm_fifo_peek (ctx->s->tx_fifo, ctx->tx_offset,
+      n_bytes_read = svm_fifo_peek (ctx->s->tx_fifo, ctx->sp.tx_offset,
 				    len_to_deq, data0);
       ASSERT (n_bytes_read > 0);
       /* Keep track of progress locally, transport is also supposed to
        * increment it independently when pushing the header */
-      ctx->tx_offset += n_bytes_read;
+      ctx->sp.tx_offset += n_bytes_read;
     }
   else
     {
@@ -756,13 +756,12 @@ session_tx_set_dequeue_params (vlib_main_t * vm, session_tx_context_t * ctx,
   if (peek_data)
     {
       /* Offset in rx fifo from where to peek data */
-      ctx->tx_offset = ctx->transport_vft->tx_fifo_offset (ctx->tc);
-      if (PREDICT_FALSE (ctx->tx_offset >= ctx->max_dequeue))
+      if (PREDICT_FALSE (ctx->sp.tx_offset >= ctx->max_dequeue))
 	{
 	  ctx->max_len_to_snd = 0;
 	  return;
 	}
-      ctx->max_dequeue -= ctx->tx_offset;
+      ctx->max_dequeue -= ctx->sp.tx_offset;
     }
   else
     {
@@ -782,34 +781,34 @@ session_tx_set_dequeue_params (vlib_main_t * vm, session_tx_context_t * ctx,
   ASSERT (ctx->max_dequeue > 0);
 
   /* Ensure we're not writing more than transport window allows */
-  if (ctx->max_dequeue < ctx->snd_space)
+  if (ctx->max_dequeue < ctx->sp.snd_space)
     {
       /* Constrained by tx queue. Try to send only fully formed segments */
-      ctx->max_len_to_snd =
-	(ctx->max_dequeue > ctx->snd_mss) ?
-	ctx->max_dequeue - ctx->max_dequeue % ctx->snd_mss : ctx->max_dequeue;
+      ctx->max_len_to_snd = (ctx->max_dequeue > ctx->sp.snd_mss) ?
+	(ctx->max_dequeue - (ctx->max_dequeue % ctx->sp.snd_mss)) :
+	ctx->max_dequeue;
       /* TODO Nagle ? */
     }
   else
     {
       /* Expectation is that snd_space0 is already a multiple of snd_mss */
-      ctx->max_len_to_snd = ctx->snd_space;
+      ctx->max_len_to_snd = ctx->sp.snd_space;
     }
 
   /* Check if we're tx constrained by the node */
-  ctx->n_segs_per_evt = ceil ((f64) ctx->max_len_to_snd / ctx->snd_mss);
+  ctx->n_segs_per_evt = ceil ((f64) ctx->max_len_to_snd / ctx->sp.snd_mss);
   if (ctx->n_segs_per_evt > max_segs)
     {
       ctx->n_segs_per_evt = max_segs;
-      ctx->max_len_to_snd = max_segs * ctx->snd_mss;
+      ctx->max_len_to_snd = max_segs * ctx->sp.snd_mss;
     }
 
   n_bytes_per_buf = vlib_buffer_get_default_data_size (vm);
   ASSERT (n_bytes_per_buf > TRANSPORT_MAX_HDRS_LEN);
-  n_bytes_per_seg = TRANSPORT_MAX_HDRS_LEN + ctx->snd_mss;
+  n_bytes_per_seg = TRANSPORT_MAX_HDRS_LEN + ctx->sp.snd_mss;
   ctx->n_bufs_per_seg = ceil ((f64) n_bytes_per_seg / n_bytes_per_buf);
-  ctx->deq_per_buf = clib_min (ctx->snd_mss, n_bytes_per_buf);
-  ctx->deq_per_first_buf = clib_min (ctx->snd_mss,
+  ctx->deq_per_buf = clib_min (ctx->sp.snd_mss, n_bytes_per_buf);
+  ctx->deq_per_first_buf = clib_min (ctx->sp.snd_mss,
 				     n_bytes_per_buf -
 				     TRANSPORT_MAX_HDRS_LEN);
 }
@@ -817,12 +816,12 @@ session_tx_set_dequeue_params (vlib_main_t * vm, session_tx_context_t * ctx,
 always_inline void
 session_tx_maybe_reschedule (session_worker_t * wrk,
 			     session_tx_context_t * ctx,
-			     session_evt_elt_t * elt, u8 is_peek)
+			     session_evt_elt_t * elt)
 {
   session_t *s = ctx->s;
 
   svm_fifo_unset_event (s->tx_fifo);
-  if (svm_fifo_max_dequeue_cons (s->tx_fifo) > (is_peek ? ctx->tx_offset : 0))
+  if (svm_fifo_max_dequeue_cons (s->tx_fifo) > ctx->sp.tx_offset)
     if (svm_fifo_set_event (s->tx_fifo))
       session_evt_add_head_old (wrk, elt);
 }
@@ -880,20 +879,23 @@ 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);
+  transport_connection_snd_params (ctx->tc, &ctx->sp);
 
-  /* This flow queue is "empty" so it should be re-evaluated before
-   * the ones that have data to send. */
-  if (!ctx->snd_space)
+  if (!ctx->sp.snd_space)
     {
-      session_evt_add_head_old (wrk, elt);
+      /* This flow queue is "empty" so it should be re-evaluated before
+       * the ones that have data to send. */
+      if (PREDICT_TRUE (!ctx->sp.flags))
+	session_evt_add_head_old (wrk, elt);
+      /* Request to postpone the session, e.g., zero-wnd and transport
+       * is not currently probing */
+      else if (ctx->sp.flags & TRANSPORT_SND_F_POSTPONE)
+	session_evt_add_old (wrk, elt);
+      /* If the deschedule flag was set, remove session from scheduler.
+       * Transport is responsible for rescheduling this session. */
+      else
+	transport_connection_deschedule (ctx->tc);
+
       return SESSION_TX_NO_DATA;
     }
 
@@ -905,9 +907,9 @@ session_tx_fifo_read_and_snd_i (session_worker_t * wrk,
 	  session_evt_add_head_old (wrk, elt);
 	  return SESSION_TX_NO_DATA;
 	}
-      snd_space = clib_min (ctx->snd_space, snd_space);
-      ctx->snd_space = snd_space >= ctx->snd_mss ?
-	snd_space - snd_space % ctx->snd_mss : snd_space;
+      snd_space = clib_min (ctx->sp.snd_space, snd_space);
+      ctx->sp.snd_space = snd_space >= ctx->sp.snd_mss ?
+	snd_space - snd_space % ctx->sp.snd_mss : snd_space;
     }
 
   /* Check how much we can pull. */
@@ -916,7 +918,7 @@ session_tx_fifo_read_and_snd_i (session_worker_t * wrk,
   if (PREDICT_FALSE (!ctx->max_len_to_snd))
     {
       transport_connection_tx_pacer_reset_bucket (ctx->tc, 0);
-      session_tx_maybe_reschedule (wrk, ctx, elt, peek_data);
+      session_tx_maybe_reschedule (wrk, ctx, elt);
       return SESSION_TX_NO_DATA;
     }
 
@@ -1019,7 +1021,7 @@ session_tx_fifo_read_and_snd_i (session_worker_t * wrk,
   if (ctx->max_len_to_snd < ctx->max_dequeue)
     session_evt_add_old (wrk, elt);
   else
-    session_tx_maybe_reschedule (wrk, ctx, elt, peek_data);
+    session_tx_maybe_reschedule (wrk, ctx, elt);
 
   if (!peek_data
       && ctx->transport_vft->transport_options.tx_type == TRANSPORT_TX_DGRAM)