path: root/net/ipv4/tcp_probe.c
diff options
authorEric Dumazet <edumazet@google.com>2014-02-26 14:02:48 -0800
committerDavid S. Miller <davem@davemloft.net>2014-02-26 17:08:40 -0500
commit740b0f1841f6e39085b711d41db9ffb07198682b (patch)
tree7befd549fc20c51bff4c79790ad4520fcc0e324e /net/ipv4/tcp_probe.c
parentnet: add skb_mstamp infrastructure (diff)
tcp: switch rtt estimations to usec resolution
Upcoming congestion controls for TCP require usec resolution for RTT estimations. Millisecond resolution is simply not enough these days. FQ/pacing in DC environments also require this change for finer control and removal of bimodal behavior due to the current hack in tcp_update_pacing_rate() for 'small rtt' TCP_CONG_RTT_STAMP is no longer needed. As Julian Anastasov pointed out, we need to keep user compatibility : tcp_metrics used to export RTT and RTTVAR in msec resolution, so we added RTT_US and RTTVAR_US. An iproute2 patch is needed to use the new attributes if provided by the kernel. In this example ss command displays a srtt of 32 usecs (10Gbit link) lpk51:~# ./ss -i dst lpk52 Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port tcp ESTAB 0 1 cubic wscale:6,6 rto:201 rtt:0.032/0.001 ato:40 mss:1448 cwnd:10 send 3620.0Mbps pacing_rate 7240.0Mbps unacked:1 rcv_rtt:993 rcv_space:29559 Updated iproute2 ip command displays : lpk51:~# ./ip tcp_metrics | grep age 561.914sec cwnd 10 rtt 274us rttvar 213us source Old binary displays : lpk51:~# ip tcp_metrics | grep age 561.914sec cwnd 10 rtt 250us rttvar 125us source With help from Julian Anastasov, Stephen Hemminger and Yuchung Cheng Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Cc: Stephen Hemminger <stephen@networkplumber.org> Cc: Yuchung Cheng <ycheng@google.com> Cc: Larry Brakmo <brakmo@google.com> Cc: Julian Anastasov <ja@ssi.bg> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_probe.c')
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/tcp_probe.c b/net/ipv4/tcp_probe.c
index 1f2d37613c9e..3b66610d4156 100644
--- a/net/ipv4/tcp_probe.c
+++ b/net/ipv4/tcp_probe.c
@@ -154,7 +154,7 @@ static void jtcp_rcv_established(struct sock *sk, struct sk_buff *skb,
p->snd_wnd = tp->snd_wnd;
p->rcv_wnd = tp->rcv_wnd;
p->ssthresh = tcp_current_ssthresh(sk);
- p->srtt = tp->srtt >> 3;
+ p->srtt = tp->srtt_us >> 3;
tcp_probe.head = (tcp_probe.head + 1) & (bufsize - 1);