From: Florin Coras <fcoras@cisco.com>
Date: Tue, 28 Nov 2023 00:03:26 +0000 (-0800)
Subject: tcp: allow unsent segments less than mss in recovery
X-Git-Tag: v24.06-rc0~112
X-Git-Url: https://gerrit.fd.io/r/gitweb?a=commitdiff_plain;h=refs%2Fchanges%2F11%2F40011%2F2;p=vpp.git

tcp: allow unsent segments less than mss in recovery

During recovery, send unsent data even if less than mss available as
application is not guaranteed to provide more.

This should speed up recovery when all data in flight was lost.

Type: improvement

Signed-off-by: Florin Coras <fcoras@cisco.com>
Change-Id: I7a3c73a0d04d93d51a5910d85450c173c3ad8e93
---

diff --git a/src/vnet/tcp/tcp_output.c b/src/vnet/tcp/tcp_output.c
index c994845de78..069c349a235 100644
--- a/src/vnet/tcp/tcp_output.c
+++ b/src/vnet/tcp/tcp_output.c
@@ -1117,7 +1117,8 @@ tcp_prepare_segment (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
       data = tcp_init_buffer (vm, *b);
       n_bytes = session_tx_fifo_peek_bytes (&tc->connection, data, offset,
 					    max_deq_bytes);
-      ASSERT (n_bytes == max_deq_bytes);
+      ASSERT (n_bytes == clib_min (max_deq_bytes, transport_max_tx_dequeue (
+						    &tc->connection)));
       b[0]->current_length = n_bytes;
       tcp_push_hdr_i (tc, *b, tc->snd_una + offset, /* compute opts */ 0,
 		      /* burst */ 0, /* update_snd_nxt */ 0);
@@ -1762,7 +1763,7 @@ tcp_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
       if (!hole)
 	{
 	  /* We are out of lost holes to retransmit so send some new data. */
-	  if (max_deq > tc->snd_mss)
+	  if (max_deq)
 	    {
 	      u32 n_segs_new;
 	      int av_wnd;
@@ -1772,7 +1773,10 @@ tcp_retransmit_sack (tcp_worker_ctx_t * wrk, tcp_connection_t * tc,
 	      av_wnd = (int) tc->snd_wnd - (tc->snd_nxt - tc->snd_una);
 	      av_wnd = clib_max (av_wnd - tc->snd_mss, 0);
 	      snd_space = clib_min (snd_space, av_wnd);
-	      snd_space = clib_min (max_deq, snd_space);
+	      /* Low bound max_deq to mss to be able to send a segment even
+	       * when it is less than mss */
+	      snd_space =
+		clib_min (clib_max (max_deq, tc->snd_mss), snd_space);
 	      burst_size = clib_min (burst_size - n_segs,
 				     snd_space / tc->snd_mss);
 	      burst_size = clib_min (burst_size, TCP_RXT_MAX_BURST);