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authorYuchung Cheng <ycheng@google.com>2015-09-18 11:36:14 -0700
committerDavid S. Miller <davem@davemloft.net>2015-09-21 16:19:01 -0700
commit0f1c28ae74bb1a34d36fca2db5161611d58b3148 (patch)
treea525dec074bcb7f5bdb79e17bdc0162637b9164a /net/ipv4/tcp_minisocks.c
parent21fe8af40024c49af37124bc7b19c5836d25695e (diff)
downloadop-kernel-dev-0f1c28ae74bb1a34d36fca2db5161611d58b3148.zip
op-kernel-dev-0f1c28ae74bb1a34d36fca2db5161611d58b3148.tar.gz
tcp: usec resolution SYN/ACK RTT
Currently SYN/ACK RTT is measured in jiffies. For LAN the SYN/ACK RTT is often measured as 0ms or sometimes 1ms, which would affect RTT estimation and min RTT samping used by some congestion control. This patch improves SYN/ACK RTT to be usec resolution if platform supports it. While the timestamping of SYN/ACK is done in request sock, the RTT measurement is carefully arranged to avoid storing another u64 timestamp in tcp_sock. For regular handshake w/o SYNACK retransmission, the RTT is sampled right after the child socket is created and right before the request sock is released (tcp_check_req() in tcp_minisocks.c) For Fast Open the child socket is already created when SYN/ACK was sent, the RTT is sampled in tcp_rcv_state_process() after processing the final ACK an right before the request socket is released. If the SYN/ACK was retransmistted or SYN-cookie was used, we rely on TCP timestamps to measure the RTT. The sample is taken at the same place in tcp_rcv_state_process() after the timestamp values are validated in tcp_validate_incoming(). Note that we do not store TS echo value in request_sock for SYN-cookies, because the value is already stored in tp->rx_opt used by tcp_ack_update_rtt(). One side benefit is that the RTT measurement now happens before initializing congestion control (of the passive side). Therefore the congestion control can use the SYN/ACK RTT. 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>
Diffstat (limited to 'net/ipv4/tcp_minisocks.c')
-rw-r--r--net/ipv4/tcp_minisocks.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 6d8795b..10933d0 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -470,7 +470,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
tcp_enable_early_retrans(newtp);
newtp->tlp_high_seq = 0;
- newtp->lsndtime = treq->snt_synack;
+ newtp->lsndtime = treq->snt_synack.stamp_jiffies;
newtp->last_oow_ack_time = 0;
newtp->total_retrans = req->num_retrans;
@@ -760,6 +760,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
if (!child)
goto listen_overflow;
+ tcp_synack_rtt_meas(child, req);
inet_csk_reqsk_queue_drop(sk, req);
inet_csk_reqsk_queue_add(sk, req, child);
/* Warning: caller must not call reqsk_put(req);
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