[PATCH][TCP]: simplify tcp_mark_lost_retrans()

[Arnd Hannemann]

Hi,

I noticed that in tcp_mark_lost_retrans the for-loop is only entered
if tcp_is_fack(tp) evaluates to true:

          if (!tcp_is_fack(tp) || !tp->retrans_out ||
              !after(received_upto, tp->lost_retrans_low) ||
              icsk->icsk_ca_state != TCP_CA_Recovery)
                  return;

Therefore the following check in the for-loop seems to be redundant,
because it always evaluates to true:

                     (tcp_is_fack(tp) ||
                      !before(received_upto,
                              ack_seq + tp->reordering * tp->mss_cache))

Did I miss something?

Best regards,
Arnd Hannemann

From: Arnd Hannemann <hannemann@xxxxxxxxxxxxxxxxxxx>

Because the for loop is only executed for FACK-enabled flows remove
redundant checks within the loop.

Signed-off-by: Arnd Hannemann <hannemann@xxxxxxxxxxxxxxxxxxx>
---
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 99b7ecb..cd8b4bd 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1178,10 +1178,7 @@ static void tcp_mark_lost_retrans(struct sock *sk)
   		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
   			continue;

-		if (after(received_upto, ack_seq) &&
-		    (tcp_is_fack(tp) ||
-		     !before(received_upto,
-			     ack_seq + tp->reordering * tp->mss_cache))) {
+		if (after(received_upto, ack_seq)) {
   			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
   			tp->retrans_out -= tcp_skb_pcount(skb);

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