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 c994845..069c349 100644 (file)
--- 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);