diff options
| author | Yuchung Cheng <ycheng@google.com> | 2015-09-18 21:36:14 +0300 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2015-09-22 02:19:01 +0300 |
| commit | 0f1c28ae74bb1a34d36fca2db5161611d58b3148 (patch) | |
| tree | a525dec074bcb7f5bdb79e17bdc0162637b9164a /net/ipv4/syncookies.c | |
| parent | 21fe8af40024c49af37124bc7b19c5836d25695e (diff) | |
| download | linux-0f1c28ae74bb1a34d36fca2db5161611d58b3148.tar.xz | |
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/syncookies.c')
| -rw-r--r-- | net/ipv4/syncookies.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index d70b1f603692..6595affded20 100644 --- a/net/ipv4/syncookies.c +++ b/net/ipv4/syncookies.c @@ -345,7 +345,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) ireq->wscale_ok = tcp_opt.wscale_ok; ireq->tstamp_ok = tcp_opt.saw_tstamp; req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; - treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; + treq->snt_synack.v64 = 0; treq->tfo_listener = false; ireq->ir_iif = sk->sk_bound_dev_if; |