diff options
| author | Eric Dumazet <edumazet@google.com> | 2014-02-22 22:25:57 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-02-24 19:13:38 -0500 |
| commit | d10473d4e3f9d1b81b50a60c8465d6f59a095c46 (patch) | |
| tree | 3210df148669c9ebae5b9f05f151123d9a6a804b /net/ipv4 | |
| parent | 7262b7b26de1495f77edbe1e71cb15b8198adb9d (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')
| -rw-r--r-- | net/ipv4/tcp_cong.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index ad37bf18ae4..2388275adb9 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); } |