tcp: update snd_congestion only during congestion

If running without sacks, if snd_una does not cover snd_congestion fast
recovery can be missed but the two heuristics from RFC6582 should avoid
that.

Also snd_congestion was used as a means of inferring if the connection
recently exited congestion while setting the persist timer but that does
not always work correctly if not congested.

Type: fix

Signed-off-by: Florin Coras <fcoras@cisco.com>
Change-Id: I94d4ac738cdd4f7f23f62e97dd63059de1cd4af9

1 files changed, 10 insertions, 22 deletions

diff --git a/src/vnet/tcp/tcp_timer.h b/src/vnet/tcp/tcp_timer.h
index 5f14a71ee7d..7f7dbf193eb 100644
--- a/src/vnet/tcp/tcp_timer.h
+++ b/src/vnet/tcp/tcp_timer.h
@@ -51,6 +51,13 @@ tcp_timer_update (tcp_timer_wheel_t * tw, tcp_connection_t * tc, u8 timer_id,
 						    timer_id, interval);
 }
 
+always_inline u8
+tcp_timer_is_active (tcp_connection_t *tc, tcp_timers_e timer)
+{
+  return tc->timers[timer] != TCP_TIMER_HANDLE_INVALID ||
+	 (tc->pending_timers & (1 << timer));
+}
+
 always_inline void
 tcp_retransmit_timer_set (tcp_timer_wheel_t * tw, tcp_connection_t * tc)
 {
@@ -74,19 +81,6 @@ tcp_persist_timer_set (tcp_timer_wheel_t * tw, tcp_connection_t * tc)
 }
 
 always_inline void
-tcp_persist_timer_update (tcp_timer_wheel_t * tw, tcp_connection_t * tc)
-{
-  u32 interval;
-
-  if (seq_leq (tc->snd_una, tc->snd_congestion + tc->burst_acked))
-    interval = 1;
-  else
-    interval = clib_max ((u32) tc->rto * TCP_TO_TIMER_TICK, 1);
-
-  tcp_timer_update (tw, tc, TCP_TIMER_PERSIST, interval);
-}
-
-always_inline void
 tcp_persist_timer_reset (tcp_timer_wheel_t * tw, tcp_connection_t * tc)
 {
   tcp_timer_reset (tw, tc, TCP_TIMER_PERSIST);
@@ -98,21 +92,15 @@ tcp_retransmit_timer_update (tcp_timer_wheel_t * tw, tcp_connection_t * tc)
   if (tc->snd_una == tc->snd_nxt)
     {
       tcp_retransmit_timer_reset (tw, tc);
-      if (tc->snd_wnd < tc->snd_mss)
-	tcp_persist_timer_update (tw, tc);
+      if (tc->snd_wnd < tc->snd_mss &&
+	  !tcp_timer_is_active (tc, TCP_TIMER_PERSIST))
+	tcp_persist_timer_set (tw, tc);
     }
   else
     tcp_timer_update (tw, tc, TCP_TIMER_RETRANSMIT,
 		      clib_max ((u32) tc->rto * TCP_TO_TIMER_TICK, 1));
 }
 
-always_inline u8
-tcp_timer_is_active (tcp_connection_t * tc, tcp_timers_e timer)
-{
-  return tc->timers[timer] != TCP_TIMER_HANDLE_INVALID
-    || (tc->pending_timers & (1 << timer));
-}
-
 always_inline void
 tcp_timer_expire_timers (tcp_timer_wheel_t * tw, f64 now)
 {