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authorEric Dumazet <edumazet@google.com>2014-02-22 22:25:57 -0800
committerDavid S. Miller <davem@davemloft.net>2014-02-24 19:13:38 -0500
commitd10473d4e3f9d1b81b50a60c8465d6f59a095c46 (patch)
tree3210df148669c9ebae5b9f05f151123d9a6a804b /net/ipv4/tcp_cong.c
parent7262b7b26de1495f77edbe1e71cb15b8198adb9d (diff)
tcp: reduce the bloat caused by tcp_is_cwnd_limited()
tcp_is_cwnd_limited() allows GSO/TSO enabled flows to increase their cwnd to allow a full size (64KB) TSO packet to be sent. Non GSO flows only allow an extra room of 3 MSS. For most flows with a BDP below 10 MSS, this results in a bloat of cwnd reaching 90, and an inflate of RTT. Thanks to TSO auto sizing, we can restrict the bloat to the number of MSS contained in a TSO packet (tp->xmit_size_goal_segs), to keep original intent without performance impact. Because we keep cwnd small, it helps to keep TSO packet size to their optimal value. Example for a 10Mbit flow, with low TCP Small queue limits (no more than 2 skb in qdisc/device tx ring) Before patch : lpk51:~# ./ss -i dst lpk52:44862 | grep cwnd cubic wscale:6,6 rto:215 rtt:15.875/2.5 mss:1448 cwnd:96 ssthresh:96 send 70.1Mbps unacked:14 rcv_space:29200 After patch : lpk51:~# ./ss -i dst lpk52:52916 | grep cwnd cubic wscale:6,6 rto:206 rtt:5.206/0.036 mss:1448 cwnd:15 ssthresh:14 send 33.4Mbps unacked:4 rcv_space:29200 Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Yuchung Cheng <ycheng@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Nandita Dukkipati <nanditad@google.com> Cc: Van Jacobson <vanj@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_cong.c')
-rw-r--r--net/ipv4/tcp_cong.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index ad37bf18ae4b..2388275adb9b 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -290,8 +290,7 @@ bool tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
left = tp->snd_cwnd - in_flight;
if (sk_can_gso(sk) &&
left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
- left * tp->mss_cache < sk->sk_gso_max_size &&
- left < sk->sk_gso_max_segs)
+ left < tp->xmit_size_goal_segs)
return true;
return left <= tcp_max_tso_deferred_mss(tp);
}