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authorYuchung Cheng <ycheng@google.com>2019-01-17 02:05:29 +0300
committerDavid S. Miller <davem@davemloft.net>2019-01-18 02:12:26 +0300
commit7f12422c4873e9b274bc151ea59cb0cdf9415cf1 (patch)
tree4fcc9a7b9a4c31aa9c470fc8fc5a4a8c59b01177
parent88f8598d0a302a08380eadefd09b9f5cb1c4c428 (diff)
downloadlinux-7f12422c4873e9b274bc151ea59cb0cdf9415cf1.tar.xz
tcp: always timestamp on every skb transmission
Previously TCP skbs are not always timestamped if the transmission failed due to memory or other local issues. This makes deciding when to abort a socket tricky and complicated because the first unacknowledged skb's timestamp may be 0 on TCP timeout. The straight-forward fix is to always timestamp skb on every transmission attempt. Also every skb retransmission needs to be flagged properly to avoid RTT under-estimation. This can happen upon receiving an ACK for the original packet and the a previous (spurious) retransmission has failed. It's worth noting that this reverts to the old time-stamping style before commit 8c72c65b426b ("tcp: update skb->skb_mstamp more carefully") which addresses a problem in computing the elapsed time of a stalled window-probing socket. The problem will be addressed differently in the next patches with a simpler approach. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Neal Cardwell <ncardwell@google.com> Reviewed-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/ipv4/tcp_output.c16
1 files changed, 8 insertions, 8 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 730bc44dbad9..57a56e205070 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -980,7 +980,6 @@ static void tcp_update_skb_after_send(struct sock *sk, struct sk_buff *skb,
{
struct tcp_sock *tp = tcp_sk(sk);
- skb->skb_mstamp_ns = tp->tcp_wstamp_ns;
if (sk->sk_pacing_status != SK_PACING_NONE) {
unsigned long rate = sk->sk_pacing_rate;
@@ -1028,7 +1027,9 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
BUG_ON(!skb || !tcp_skb_pcount(skb));
tp = tcp_sk(sk);
-
+ prior_wstamp = tp->tcp_wstamp_ns;
+ tp->tcp_wstamp_ns = max(tp->tcp_wstamp_ns, tp->tcp_clock_cache);
+ skb->skb_mstamp_ns = tp->tcp_wstamp_ns;
if (clone_it) {
TCP_SKB_CB(skb)->tx.in_flight = TCP_SKB_CB(skb)->end_seq
- tp->snd_una;
@@ -1045,11 +1046,6 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
return -ENOBUFS;
}
- prior_wstamp = tp->tcp_wstamp_ns;
- tp->tcp_wstamp_ns = max(tp->tcp_wstamp_ns, tp->tcp_clock_cache);
-
- skb->skb_mstamp_ns = tp->tcp_wstamp_ns;
-
inet = inet_sk(sk);
tcb = TCP_SKB_CB(skb);
memset(&opts, 0, sizeof(opts));
@@ -2937,12 +2933,16 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
}
+ /* To avoid taking spuriously low RTT samples based on a timestamp
+ * for a transmit that never happened, always mark EVER_RETRANS
+ */
+ TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
+
if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RETRANS_CB_FLAG))
tcp_call_bpf_3arg(sk, BPF_SOCK_OPS_RETRANS_CB,
TCP_SKB_CB(skb)->seq, segs, err);
if (likely(!err)) {
- TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
trace_tcp_retransmit_skb(sk, skb);
} else if (err != -EBUSY) {
NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL, segs);