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authorYuchung Cheng <ycheng@google.com>2013-07-22 16:20:46 -0700
committerDavid S. Miller <davem@davemloft.net>2013-07-22 17:53:42 -0700
commit5b08e47caf1f2034a3a5b566bbccc8b0be3961ca (patch)
tree5cdd3ad01a4b854c80bad612051ac7ce7140e948 /net/ipv4
parent375fe02c91792917aa26d68a87ab110d1937f44e (diff)
downloadlinux-5b08e47caf1f2034a3a5b566bbccc8b0be3961ca.tar.bz2
tcp: prefer packet timing to TS-ECR for RTT
Prefer packet timings to TS-ecr for RTT measurements when both sources are available. That's because broken middle-boxes and remote peer can return packets with corrupted TS ECR fields. Similarly most congestion controls that require RTT signals favor timing-based sources as well. Also check for bad TS ECR values to avoid RTT blow-ups. It has happened on production Web servers. Signed-off-by: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4')
-rw-r--r--net/ipv4/tcp_input.c67
1 files changed, 18 insertions, 49 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index b531710596ec..c7398f05d12b 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2792,65 +2792,36 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
tcp_xmit_retransmit_queue(sk);
}
-void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
+static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
+ s32 seq_rtt)
{
- tcp_rtt_estimator(sk, seq_rtt);
- tcp_set_rto(sk);
- inet_csk(sk)->icsk_backoff = 0;
-}
-EXPORT_SYMBOL(tcp_valid_rtt_meas);
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ /* Prefer RTT measured from ACK's timing to TS-ECR. This is because
+ * broken middle-boxes or peers may corrupt TS-ECR fields. But
+ * Karn's algorithm forbids taking RTT if some retransmitted data
+ * is acked (RFC6298).
+ */
+ if (flag & FLAG_RETRANS_DATA_ACKED)
+ seq_rtt = -1;
-/* Read draft-ietf-tcplw-high-performance before mucking
- * with this code. (Supersedes RFC1323)
- */
-static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
-{
/* RTTM Rule: A TSecr value received in a segment is used to
* update the averaged RTT measurement only if the segment
* acknowledges some new data, i.e., only if it advances the
* left edge of the send window.
- *
* See draft-ietf-tcplw-high-performance-00, section 3.3.
- * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
- *
- * Changed: reset backoff as soon as we see the first valid sample.
- * If we do not, we get strongly overestimated rto. With timestamps
- * samples are accepted even from very old segments: f.e., when rtt=1
- * increases to 8, we retransmit 5 times and after 8 seconds delayed
- * answer arrives rto becomes 120 seconds! If at least one of segments
- * in window is lost... Voila. --ANK (010210)
*/
- struct tcp_sock *tp = tcp_sk(sk);
+ if (seq_rtt < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
+ seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
- tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr);
-}
-
-static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
-{
- /* We don't have a timestamp. Can only use
- * packets that are not retransmitted to determine
- * rtt estimates. Also, we must not reset the
- * backoff for rto until we get a non-retransmitted
- * packet. This allows us to deal with a situation
- * where the network delay has increased suddenly.
- * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
- */
-
- if (flag & FLAG_RETRANS_DATA_ACKED)
+ if (seq_rtt < 0)
return;
- tcp_valid_rtt_meas(sk, seq_rtt);
-}
+ tcp_rtt_estimator(sk, seq_rtt);
+ tcp_set_rto(sk);
-static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
- const s32 seq_rtt)
-{
- const struct tcp_sock *tp = tcp_sk(sk);
- /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
- if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
- tcp_ack_saw_tstamp(sk, flag);
- else if (seq_rtt >= 0)
- tcp_ack_no_tstamp(sk, seq_rtt, flag);
+ /* RFC6298: only reset backoff on valid RTT measurement. */
+ inet_csk(sk)->icsk_backoff = 0;
}
/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
@@ -2989,8 +2960,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
if (sacked & TCPCB_SACKED_RETRANS)
tp->retrans_out -= acked_pcount;
flag |= FLAG_RETRANS_DATA_ACKED;
- ca_seq_rtt = -1;
- seq_rtt = -1;
} else {
ca_seq_rtt = now - scb->when;
last_ackt = skb->tstamp;