From: Eric Dumazet Date: Sun, 23 Feb 2014 06:25:57 +0000 (-0800) Subject: tcp: reduce the bloat caused by tcp_is_cwnd_limited() X-Git-Tag: v3.14-rc6~30^2~40 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d10473d4e3f9d1b81b50a60c8465d6f59a095c46;p=pandora-kernel.git 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 Cc: Yuchung Cheng Cc: Neal Cardwell Cc: Nandita Dukkipati Cc: Van Jacobson Acked-by: Neal Cardwell Signed-off-by: David S. Miller --- Reading git-diff-tree failed