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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
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')
-rw-r--r--net/ipv4/syncookies.c2
-rw-r--r--net/ipv4/tcp_input.c29
-rw-r--r--net/ipv4/tcp_minisocks.c3
3 files changed, 17 insertions, 17 deletions
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index d70b1f6..6595aff 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;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a62e9c7..497adf5 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2953,21 +2953,21 @@ static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
}
/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
-static void tcp_synack_rtt_meas(struct sock *sk, const u32 synack_stamp)
+void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
{
- struct tcp_sock *tp = tcp_sk(sk);
- long seq_rtt_us = -1L;
+ long rtt_us = -1L;
- if (synack_stamp && !tp->total_retrans)
- seq_rtt_us = jiffies_to_usecs(tcp_time_stamp - synack_stamp);
+ if (req && !req->num_retrans && tcp_rsk(req)->snt_synack.v64) {
+ struct skb_mstamp now;
- /* If the ACK acks both the SYNACK and the (Fast Open'd) data packets
- * sent in SYN_RECV, SYNACK RTT is the smooth RTT computed in tcp_ack()
- */
- if (!tp->srtt_us)
- tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, seq_rtt_us, -1L);
+ skb_mstamp_get(&now);
+ rtt_us = skb_mstamp_us_delta(&now, &tcp_rsk(req)->snt_synack);
+ }
+
+ tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L);
}
+
static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
@@ -5706,7 +5706,6 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
struct request_sock *req;
int queued = 0;
bool acceptable;
- u32 synack_stamp;
tp->rx_opt.saw_tstamp = 0;
@@ -5785,15 +5784,16 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
if (!acceptable)
return 1;
+ if (!tp->srtt_us)
+ tcp_synack_rtt_meas(sk, req);
+
/* Once we leave TCP_SYN_RECV, we no longer need req
* so release it.
*/
if (req) {
- synack_stamp = tcp_rsk(req)->snt_synack;
tp->total_retrans = req->num_retrans;
reqsk_fastopen_remove(sk, req, false);
} else {
- synack_stamp = tp->lsndtime;
/* Make sure socket is routed, for correct metrics. */
icsk->icsk_af_ops->rebuild_header(sk);
tcp_init_congestion_control(sk);
@@ -5816,7 +5816,6 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
- tcp_synack_rtt_meas(sk, synack_stamp);
if (tp->rx_opt.tstamp_ok)
tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
@@ -6027,7 +6026,7 @@ static void tcp_openreq_init(struct request_sock *req,
req->cookie_ts = 0;
tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
- tcp_rsk(req)->snt_synack = tcp_time_stamp;
+ skb_mstamp_get(&tcp_rsk(req)->snt_synack);
tcp_rsk(req)->last_oow_ack_time = 0;
req->mss = rx_opt->mss_clamp;
req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
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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