tcp: a small refactor of RACK loss detection

Refactor the RACK loop to improve readability and speed up the checks.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_recovery.c b/net/ipv4/tcp_recovery.c
index 8aa56ca..cda6074 100644 (file)
--- a/net/ipv4/tcp_recovery.c
+++ b/net/ipv4/tcp_recovery.c
@@ -61,32 +61,28 @@ static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout)
        list_for_each_entry_safe(skb, n, &tp->tsorted_sent_queue,
                                 tcp_tsorted_anchor) {
                struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
+               s32 remaining;
 
-               if (tcp_rack_sent_after(tp->rack.mstamp, skb->skb_mstamp,
-                                       tp->rack.end_seq, scb->end_seq)) {
-                       /* Step 3 in draft-cheng-tcpm-rack-00.txt:
-                        * A packet is lost if its elapsed time is beyond
-                        * the recent RTT plus the reordering window.
-                        */
-                       u32 elapsed = tcp_stamp_us_delta(tp->tcp_mstamp,
-                                                        skb->skb_mstamp);
-                       s32 remaining = tp->rack.rtt_us + reo_wnd - elapsed;
-
-                       if (remaining < 0) {
-                               tcp_rack_mark_skb_lost(sk, skb);
-                               list_del_init(&skb->tcp_tsorted_anchor);
-                               continue;
-                       }
-
-                       /* Skip ones marked lost but not yet retransmitted */
-                       if ((scb->sacked & TCPCB_LOST) &&
-                           !(scb->sacked & TCPCB_SACKED_RETRANS))
-                               continue;
+               /* Skip ones marked lost but not yet retransmitted */
+               if ((scb->sacked & TCPCB_LOST) &&
+                   !(scb->sacked & TCPCB_SACKED_RETRANS))
+                       continue;
 
+               if (!tcp_rack_sent_after(tp->rack.mstamp, skb->skb_mstamp,
+                                        tp->rack.end_seq, scb->end_seq))
+                       break;
+
+               /* A packet is lost if it has not been s/acked beyond
+                * the recent RTT plus the reordering window.
+                */
+               remaining = tp->rack.rtt_us + reo_wnd -
+                           tcp_stamp_us_delta(tp->tcp_mstamp, skb->skb_mstamp);
+               if (remaining < 0) {
+                       tcp_rack_mark_skb_lost(sk, skb);
+                       list_del_init(&skb->tcp_tsorted_anchor);
+               } else {
                        /* Record maximum wait time (+1 to avoid 0) */
                        *reo_timeout = max_t(u32, *reo_timeout, 1 + remaining);
-               } else {
-                       break;
                }
        }
 }