tcp: track reorder with sacks

Type: feature

Change-Id: I041bff2e8d589c171661de286fa1503531dff891
Signed-off-by: Florin Coras <fcoras@cisco.com>

diff --git a/src/plugins/unittest/tcp_test.c b/src/plugins/unittest/tcp_test.c
index b98d360..3db0405 100644 (file)
--- a/src/plugins/unittest/tcp_test.c
+++ b/src/plugins/unittest/tcp_test.c
@@ -505,7 +505,9 @@ tcp_test_sack_rx (vlib_main_t * vm, unformat_input_t * input)
            sb->last_sacked_bytes);
   TCP_TEST ((sb->last_bytes_delivered == 0), "last bytes delivered %d",
            sb->last_bytes_delivered);
+  /* Hole should be split in 2 lost holes that add up to 300 */
   TCP_TEST ((sb->lost_bytes == 300), "lost bytes %u", sb->lost_bytes);
+  TCP_TEST ((sb->reorder == 7), "reorder %u", sb->reorder);
 
   /*
    * Ack [100 300] in two steps
@@ -590,7 +592,9 @@ tcp_test_sack_rx (vlib_main_t * vm, unformat_input_t * input)
            sb->last_sacked_bytes);
   TCP_TEST ((sb->last_bytes_delivered == 0), "last bytes delivered %d",
            sb->last_bytes_delivered);
-  TCP_TEST ((sb->lost_bytes == 200), "lost bytes %u", sb->lost_bytes);
+  /* No bytes lost because of reorder */
+  TCP_TEST ((sb->lost_bytes == 0), "lost bytes %u", sb->lost_bytes);
+  TCP_TEST ((sb->reorder == 7), "reorder %u", sb->reorder);
   TCP_TEST ((!sb->is_reneging), "is not reneging");
 
   /*

diff --git a/src/vnet/tcp/tcp.c b/src/vnet/tcp/tcp.c
index 938a863..1563be4 100644 (file)
--- a/src/vnet/tcp/tcp.c
+++ b/src/vnet/tcp/tcp.c
@@ -925,17 +925,21 @@ tcp_snd_space_inline (tcp_connection_t * tc)
    * to force the peer to send enough dupacks to start retransmitting as
    * per Limited Transmit (RFC3042)
    */
-  if (PREDICT_FALSE (tc->rcv_dupacks != 0 || tc->sack_sb.sacked_bytes))
+  if (PREDICT_FALSE (tc->rcv_dupacks || tc->sack_sb.sacked_bytes))
     {
-      if (tc->limited_transmit != tc->snd_nxt
-         && (seq_lt (tc->limited_transmit, tc->snd_nxt - 2 * tc->snd_mss)
-             || seq_gt (tc->limited_transmit, tc->snd_nxt)))
+      int snt_limited, n_pkts;
+
+      n_pkts = tcp_opts_sack_permitted (&tc->rcv_opts)
+       ? tc->sack_sb.reorder - 1 : 2;
+
+      if ((seq_lt (tc->limited_transmit, tc->snd_nxt - n_pkts * tc->snd_mss)
+          || seq_gt (tc->limited_transmit, tc->snd_nxt)))
        tc->limited_transmit = tc->snd_nxt;
 
       ASSERT (seq_leq (tc->limited_transmit, tc->snd_nxt));
 
-      int snt_limited = tc->snd_nxt - tc->limited_transmit;
-      snd_space = clib_max ((int) 2 * tc->snd_mss - snt_limited, 0);
+      snt_limited = tc->snd_nxt - tc->limited_transmit;
+      snd_space = clib_max (n_pkts * tc->snd_mss - snt_limited, 0);
     }
   return tcp_round_snd_space (tc, snd_space);
 }

diff --git a/src/vnet/tcp/tcp_cli.c b/src/vnet/tcp/tcp_cli.c
index 6ad2425..edd4d2d 100644 (file)
--- a/src/vnet/tcp/tcp_cli.c
+++ b/src/vnet/tcp/tcp_cli.c
@@ -341,9 +341,10 @@ format_tcp_scoreboard (u8 * s, va_list * args)
              " rxt_sacked %u\n",
              sb->sacked_bytes, sb->last_sacked_bytes, sb->lost_bytes,
              sb->last_lost_bytes, sb->rxt_sacked);
-  s = format (s, "%Ulast_delivered %u high_sacked %u is_reneging %u\n",
+  s = format (s, "%Ulast_delivered %u high_sacked %u is_reneging %u",
              format_white_space, indent, sb->last_bytes_delivered,
              sb->high_sacked - tc->iss, sb->is_reneging);
+  s = format (s, " reorder %u\n", sb->reorder);
   s = format (s, "%Ucur_rxt_hole %u high_rxt %u rescue_rxt %u",
              format_white_space, indent, sb->cur_rxt_hole,
              sb->high_rxt - tc->iss, sb->rescue_rxt - tc->iss);

diff --git a/src/vnet/tcp/tcp_input.c b/src/vnet/tcp/tcp_input.c
index 5fa7bf2..de9d891 100644 (file)
--- a/src/vnet/tcp/tcp_input.c
+++ b/src/vnet/tcp/tcp_input.c
@@ -689,7 +689,7 @@ tcp_cc_init_congestion (tcp_connection_t * tc)
    * three segments that have left the network and should've been
    * buffered at the receiver XXX */
   if (!tcp_opts_sack_permitted (&tc->rcv_opts))
-    tc->cwnd += 3 * tc->snd_mss;
+    tc->cwnd += TCP_DUPACK_THRESHOLD * tc->snd_mss;
 
   tc->fr_occurences += 1;
   TCP_EVT (TCP_EVT_CC_EVT, tc, 4);
@@ -720,14 +720,6 @@ tcp_cc_is_spurious_retransmit (tcp_connection_t * tc)
   return (tcp_cc_is_spurious_timeout_rxt (tc));
 }
 
-static inline u8
-tcp_should_fastrecover_sack (tcp_connection_t * tc)
-{
-  return (tc->sack_sb.lost_bytes
-         || ((TCP_DUPACK_THRESHOLD - 1) * tc->snd_mss
-             < tc->sack_sb.sacked_bytes));
-}
-
 static inline u8
 tcp_should_fastrecover (tcp_connection_t * tc, u8 has_sack)
 {
@@ -752,8 +744,7 @@ tcp_should_fastrecover (tcp_connection_t * tc, u8 has_sack)
          return 0;
        }
     }
-  return ((tc->rcv_dupacks == TCP_DUPACK_THRESHOLD)
-         || tcp_should_fastrecover_sack (tc));
+  return tc->sack_sb.lost_bytes || tc->rcv_dupacks >= tc->sack_sb.reorder;
 }
 
 static int

diff --git a/src/vnet/tcp/tcp_output.c b/src/vnet/tcp/tcp_output.c
index e9bff5b..294b18c 100644 (file)
--- a/src/vnet/tcp/tcp_output.c
+++ b/src/vnet/tcp/tcp_output.c
@@ -1290,6 +1290,7 @@ tcp_cc_init_rxt_timeout (tcp_connection_t * tc)
   tc->rtt_ts = 0;
   tc->cwnd_acc_bytes = 0;
   tc->tr_occurences += 1;
+  tc->sack_sb.reorder = TCP_DUPACK_THRESHOLD;
   tcp_recovery_on (tc);
 }
 

diff --git a/src/vnet/tcp/tcp_sack.c b/src/vnet/tcp/tcp_sack.c
index b9e1166..8f51b51 100644 (file)
--- a/src/vnet/tcp/tcp_sack.c
+++ b/src/vnet/tcp/tcp_sack.c
@@ -88,10 +88,23 @@ scoreboard_insert_hole (sack_scoreboard_t * sb, u32 prev_index,
 }
 
 always_inline void
-scoreboard_update_sacked_rxt (sack_scoreboard_t * sb, u32 start, u32 end,
-                             u8 has_rxt)
+scoreboard_update_sacked (sack_scoreboard_t * sb, u32 start, u32 end,
+                         u8 has_rxt, u16 snd_mss)
 {
-  if (!has_rxt || seq_geq (start, sb->high_rxt))
+  if (!has_rxt)
+    {
+      /* Sequence was not retransmitted but it was sacked. Estimate reorder
+       * only if not in congestion recovery */
+      if (seq_lt (start, sb->high_sacked))
+       {
+         u32 reord = (sb->high_sacked - start + snd_mss - 1) / snd_mss;
+         reord = clib_min (reord, TCP_MAX_SACK_REORDER);
+         sb->reorder = clib_max (sb->reorder, reord);
+       }
+      return;
+    }
+
+  if (seq_geq (start, sb->high_rxt))
     return;
 
   sb->rxt_sacked +=
@@ -125,8 +138,14 @@ scoreboard_update_bytes (sack_scoreboard_t * sb, u32 ack, u32 snd_mss)
       blks = 1;
     }
 
-  while (sacked < (TCP_DUPACK_THRESHOLD - 1) * snd_mss
-        && blks < TCP_DUPACK_THRESHOLD)
+  /* As per RFC 6675 a sequence number is lost if:
+   *   DupThresh discontiguous SACKed sequences have arrived above
+   *   'SeqNum' or more than (DupThresh - 1) * SMSS bytes with sequence
+   *   numbers greater than 'SeqNum' have been SACKed.
+   * To avoid spurious retransmits, use reordering estimate instead of
+   * DupThresh to detect loss.
+   */
+  while (sacked <= (sb->reorder - 1) * snd_mss && blks < sb->reorder)
     {
       if (right->is_lost)
        sb->lost_bytes += scoreboard_hole_bytes (right);
@@ -251,6 +270,7 @@ scoreboard_init (sack_scoreboard_t * sb)
   sb->head = TCP_INVALID_SACK_HOLE_INDEX;
   sb->tail = TCP_INVALID_SACK_HOLE_INDEX;
   sb->cur_rxt_hole = TCP_INVALID_SACK_HOLE_INDEX;
+  sb->reorder = TCP_DUPACK_THRESHOLD;
 }
 
 void
@@ -270,6 +290,7 @@ scoreboard_clear (sack_scoreboard_t * sb)
   sb->last_lost_bytes = 0;
   sb->cur_rxt_hole = TCP_INVALID_SACK_HOLE_INDEX;
   sb->is_reneging = 0;
+  sb->reorder = TCP_DUPACK_THRESHOLD;
 }
 
 void
@@ -307,7 +328,7 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
   sack_scoreboard_hole_t *hole, *next_hole;
   sack_scoreboard_t *sb = &tc->sack_sb;
   sack_block_t *blk, *rcv_sacks;
-  u32 blk_index = 0, i, j;
+  u32 blk_index = 0, i, j, high_sacked;
   u8 has_rxt;
 
   sb->last_sacked_bytes = 0;
@@ -391,8 +412,9 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
          hole = scoreboard_insert_hole (sb, TCP_INVALID_SACK_HOLE_INDEX,
                                         tc->snd_una, tc->snd_nxt);
          sb->tail = scoreboard_hole_index (sb, hole);
+         sb->high_sacked = tc->snd_una;
        }
-      sb->high_sacked = rcv_sacks[vec_len (rcv_sacks) - 1].end;
+      high_sacked = rcv_sacks[vec_len (rcv_sacks) - 1].end;
     }
   else
     {
@@ -412,11 +434,10 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
                                      tc->snd_nxt);
            }
        }
-
       /* Keep track of max byte sacked for when the last hole
        * is acked */
-      sb->high_sacked = seq_max (rcv_sacks[vec_len (rcv_sacks) - 1].end,
-                                sb->high_sacked);
+      high_sacked = seq_max (rcv_sacks[vec_len (rcv_sacks) - 1].end,
+                            sb->high_sacked);
     }
 
   /* Walk the holes with the SACK blocks */
@@ -442,7 +463,8 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
              /* If covered by ack, compute delivered bytes */
              if (blk->end == ack)
                {
-                 u32 sacked = next_hole ? next_hole->start : sb->high_sacked;
+                 u32 sacked = next_hole ? next_hole->start :
+                   seq_max (sb->high_sacked, hole->end);
                  if (PREDICT_FALSE (seq_lt (ack, sacked)))
                    {
                      sb->last_bytes_delivered += ack - hole->end;
@@ -454,8 +476,8 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
                      sb->is_reneging = 0;
                    }
                }
-             scoreboard_update_sacked_rxt (sb, hole->start, hole->end,
-                                           has_rxt);
+             scoreboard_update_sacked (sb, hole->start, hole->end,
+                                       has_rxt, tc->snd_mss);
              scoreboard_remove_hole (sb, hole);
              hole = next_hole;
            }
@@ -464,8 +486,8 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
            {
              if (seq_gt (blk->end, hole->start))
                {
-                 scoreboard_update_sacked_rxt (sb, hole->start, blk->end,
-                                               has_rxt);
+                 scoreboard_update_sacked (sb, hole->start, blk->end,
+                                           has_rxt, tc->snd_mss);
                  hole->start = blk->end;
                }
              blk_index++;
@@ -482,23 +504,25 @@ tcp_rcv_sacks (tcp_connection_t * tc, u32 ack)
              /* Pool might've moved */
              hole = scoreboard_get_hole (sb, hole_index);
              hole->end = blk->start;
+             next_hole->is_lost = hole->is_lost;
 
-             scoreboard_update_sacked_rxt (sb, blk->start, blk->end,
-                                           has_rxt);
+             scoreboard_update_sacked (sb, blk->start, blk->end,
+                                       has_rxt, tc->snd_mss);
 
              blk_index++;
              ASSERT (hole->next == scoreboard_hole_index (sb, next_hole));
            }
          else if (seq_lt (blk->start, hole->end))
            {
-             scoreboard_update_sacked_rxt (sb, blk->start, hole->end,
-                                           has_rxt);
+             scoreboard_update_sacked (sb, blk->start, hole->end,
+                                       has_rxt, tc->snd_mss);
              hole->end = blk->start;
            }
          hole = scoreboard_next_hole (sb, hole);
        }
     }
 
+  sb->high_sacked = high_sacked;
   scoreboard_update_bytes (sb, ack, tc->snd_mss);
 
   ASSERT (sb->last_sacked_bytes <= sb->sacked_bytes || tcp_in_recovery (tc));

diff --git a/src/vnet/tcp/tcp_types.h b/src/vnet/tcp/tcp_types.h
index d7bcac5..027f0e6 100644 (file)
--- a/src/vnet/tcp/tcp_types.h
+++ b/src/vnet/tcp/tcp_types.h
@@ -151,6 +151,7 @@ typedef enum tcp_connection_flag_
 #define TCP_SCOREBOARD_TRACE (0)
 #define TCP_MAX_SACK_BLOCKS 255        /**< Max number of SACK blocks stored */
 #define TCP_INVALID_SACK_HOLE_INDEX ((u32)~0)
+#define TCP_MAX_SACK_REORDER 300
 
 typedef struct _scoreboard_trace_elt
 {
@@ -185,7 +186,8 @@ typedef struct _sack_scoreboard
   u32 lost_bytes;                      /**< Bytes lost as per RFC6675 */
   u32 last_lost_bytes;                 /**< Number of bytes last lost */
   u32 cur_rxt_hole;                    /**< Retransmitting from this hole */
-  u8 is_reneging;
+  u32 reorder;                         /**< Estimate of segment reordering */
+  u8 is_reneging;                      /**< Flag set if peer is reneging*/
 
 #if TCP_SCOREBOARD_TRACE
   scoreboard_trace_elt_t *trace;