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| author |   Yuchung Cheng <ycheng@google.com> | 2015-09-18 11:36:14 -0700 |
|---|---|---|
| committer |   David S. Miller <davem@davemloft.net> | 2015-09-21 16:19:01 -0700 |
| commit | 0f1c28ae74bb1a34d36fca2db5161611d58b3148 (patch) | |
| tree | a525dec074bcb7f5bdb79e17bdc0162637b9164a /include/net/tcp.h | |
| parent | Merge branch 's390-next' (diff) | |
| download | linux-dev-0f1c28ae74bb1a34d36fca2db5161611d58b3148.tar.xz linux-dev-0f1c28ae74bb1a34d36fca2db5161611d58b3148.zip | |
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/net/tcp.h')
| -rw-r--r-- | include/net/tcp.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h index 0cab28cd43a9..5cf9672c13e2 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -565,6 +565,7 @@ bool tcp_schedule_loss_probe(struct sock *sk); /* tcp_input.c */ void tcp_resume_early_retransmit(struct sock *sk); void tcp_rearm_rto(struct sock *sk); +void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req); void tcp_reset(struct sock *sk); /* tcp_timer.c */ |