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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>
This commit is contained in:
Yuchung Cheng 2017-10-04 13:00:00 -07:00 committed by David S. Miller
parent 043b87d759
commit bef0622308
1 changed files with 17 additions and 21 deletions
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38
net/ipv4/tcp_recovery.c
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@ -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;
/* Skip ones marked lost but not yet retransmitted */
if ((scb->sacked & TCPCB_LOST) &&
!(scb->sacked & TCPCB_SACKED_RETRANS))
continue;
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;
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;
}
}
}