tree 6a4c6198ffceb8b241c4d221aee16cf815b3152b
parent a9e050f4e7f9d36afe0dcc0bddba864ee442715e
author Eric Dumazet <edumazet@google.com> 1344251083 +0000
committer David S. Miller <davem@davemloft.net> 1344287674 -0700

tcp: ecn: dont delay ACKS after CE

While playing with CoDel and ECN marking, I discovered a
non optimal behavior of receiver of CE (Congestion Encountered)
segments.

In pathological cases, sender has reduced its cwnd to low values,
and receiver delays its ACK (by 40 ms).

While RFC 3168 6.1.3 (The TCP Receiver) doesn't explicitly recommend
to send immediate ACKS, we believe its better to not delay ACKS, because
a CE segment should give same signal than a dropped segment, and its
quite important to reduce RTT to give ECE/CWR signals as fast as
possible.

Note we already call tcp_enter_quickack_mode() from TCP_ECN_check_ce()
if we receive a retransmit, for the same reason.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>