Currently the retransmission stats are not incremented if the
retransmit fails locally. But we always increment the other packet
counters that track total packet/bytes sent. Awkwardly while we
don't count these failed retransmits in RETRANSSEGS, we do count
them in FAILEDRETRANS.
If the qdisc is dropping many packets this could under-estimate
TCP retransmission rate substantially from both SNMP or per-socket
TCP_INFO stats. This patch changes this by always incrementing
retransmission stats on retransmission attempts and failures.
Another motivation is to properly track retransmists in
SCM_TIMESTAMPING_OPT_STATS. Since SCM_TSTAMP_SCHED collection is
triggered in tcp_transmit_skb(), If tp->total_retrans is incremented
after the function, we'll always mis-count by the amount of the
latest retransmission.
Signed-off-by: Yuchung Cheng <ych...@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com>
Acked-by: Neal Cardwell <ncardw...@google.com>
Acked-by: Eric Dumazet <eduma...@google.com>
---
net/ipv4/tcp_output.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 671c69535671..7b2d8762f15f 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2771,6 +2771,13 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff
*skb, int segs)
if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
tcp_ecn_clear_syn(sk, skb);
+ /* Update global and local TCP statistics. */
+ segs = tcp_skb_pcount(skb);
+ TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
+ if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
+ __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
+ tp->total_retrans += segs;
+
/* make sure skb->data is aligned on arches that require it
* and check if ack-trimming & collapsing extended the headroom
* beyond what csum_start can cover.
@@ -2788,14 +2795,9 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff
*skb, int segs)
}
if (likely(!err)) {
- segs = tcp_skb_pcount(skb);
-
TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
- /* Update global TCP statistics. */
- TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs);
- if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
- __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
- tp->total_retrans += segs;
+ } else if (err != -EBUSY) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
}
return err;
}
@@ -2818,8 +2820,6 @@ int tcp_retransmit_skb(struct sock *sk, struct sk_buff
*skb, int segs)
if (!tp->retrans_stamp)
tp->retrans_stamp = tcp_skb_timestamp(skb);
- } else if (err != -EBUSY) {
- NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
}
if (tp->undo_retrans < 0)
--
2.11.0.483.g087da7b7c-goog
