tcp: simpler NewReno implementation

This is a rewrite of NewReno loss recovery implementation that is
simpler and standalone for readability and better performance by
using less states.

Note that NewReno refers to RFC6582 as a modification to the fast
recovery algorithm. It is used only if the connection does not
support SACK in Linux. It should not to be confused with the Reno
(AIMD) congestion control.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Priyaranjan Jha <priyarjha@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 8 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index ccbe04f80040..076206873e3e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2223,9 +2223,7 @@ static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
 {
         struct tcp_sock *tp = tcp_sk(sk);
 
-        if (tcp_is_reno(tp)) {
-                tcp_mark_head_lost(sk, 1, 1);
-        } else {
+        if (tcp_is_sack(tp)) {
                 int sacked_upto = tp->sacked_out - tp->reordering;
                 if (sacked_upto >= 0)
                         tcp_mark_head_lost(sk, sacked_upto, 0);
@@ -2723,11 +2721,16 @@ static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una)
         return false;
 }
 
-static void tcp_rack_identify_loss(struct sock *sk, int *ack_flag)
+static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
 {
         struct tcp_sock *tp = tcp_sk(sk);
 
-        if (tcp_is_rack(sk)) {
+        if (tcp_rtx_queue_empty(sk))
+                return;
+
+        if (unlikely(tcp_is_reno(tp))) {
+                tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
+        } else if (tcp_is_rack(sk)) {
                 u32 prior_retrans = tp->retrans_out;
 
                 tcp_rack_mark_lost(sk);
@@ -2823,11 +2826,11 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
                         tcp_try_keep_open(sk);
                         return;
                 }
-                tcp_rack_identify_loss(sk, ack_flag);
+                tcp_identify_packet_loss(sk, ack_flag);
                 break;
         case TCP_CA_Loss:
                 tcp_process_loss(sk, flag, is_dupack, rexmit);
-                tcp_rack_identify_loss(sk, ack_flag);
+                tcp_identify_packet_loss(sk, ack_flag);
                 if (!(icsk->icsk_ca_state == TCP_CA_Open ||
                       (*ack_flag & FLAG_LOST_RETRANS)))
                         return;
@@ -2844,7 +2847,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
                 if (icsk->icsk_ca_state <= TCP_CA_Disorder)
                         tcp_try_undo_dsack(sk);
 
-                tcp_rack_identify_loss(sk, ack_flag);
+                tcp_identify_packet_loss(sk, ack_flag);
                 if (!tcp_time_to_recover(sk, flag)) {
                         tcp_try_to_open(sk, flag);
                         return;