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tcp: tso: allow CA_CWR state in tcp_tso_should_defer()

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Another TCP issue is triggered by ECN.

Under pressure, receiver gets ECN marks, and send back ACK packets
with ECE TCP flag. Senders enter CA_CWR state.

In this state, tcp_tso_should_defer() is short cut :

if (icsk->icsk_ca_state != TCP_CA_Open)
    goto send_now;

This means that about all ACK packets we receive are triggering
a partial send, and because cwnd is kept small, we can only send
a small amount of data for each incoming ACK,
which in return generate more ACK packets.

Allowing CA_Open and CA_CWR states to enable TSO defer in
tcp_tso_should_defer() brings performance back :
TSO autodefer has more chance to defer under pressure.

This patch increases TSO and LRO/GRO efficiency back to normal levels,
and does not impact overall ECN behavior.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2015-02-26 14:10:20 -08:00 committed by David S. Miller
parent 50c8339e92
commit a0ea700e40
1 changed files with 1 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
net/ipv4/tcp_output.c
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@ -1762,7 +1762,7 @@ static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
goto send_now; goto send_now;
if (icsk->icsk_ca_state != TCP_CA_Open) if (!((1 << icsk->icsk_ca_state) & (TCPF_CA_Open | TCPF_CA_CWR)))
goto send_now; goto send_now;
/* Avoid bursty behavior by allowing defer /* Avoid bursty behavior by allowing defer