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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 /include/linux/tcp.h
parent21fe8af40024c49af37124bc7b19c5836d25695e (diff)
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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 'include/linux/tcp.h')
-rw-r--r--include/linux/tcp.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 937b97893d5f..fcb573be75d9 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -112,11 +112,11 @@ struct tcp_request_sock_ops;
struct tcp_request_sock {
struct inet_request_sock req;
const struct tcp_request_sock_ops *af_specific;
+ struct skb_mstamp snt_synack; /* first SYNACK sent time */
bool tfo_listener;
u32 txhash;
u32 rcv_isn;
u32 snt_isn;
- u32 snt_synack; /* synack sent time */
u32 last_oow_ack_time; /* last SYNACK */
u32 rcv_nxt; /* the ack # by SYNACK. For
* FastOpen it's the seq#