Bloat » Cerowrt

---------- Forwarded message ----------
From: Neal Cardwell <ncardwell@google.com>
Date: Sun, Apr 29, 2012 at 8:49 PM
Subject: Re: [PATCH] tcp: fix infinite cwnd in tcp_complete_cwr()
To: Yuchung Cheng <ycheng@google.com>
Cc: davem@davemloft.net, ilpo.jarvinen@helsinki.fi,
nanditad@google.com, netdev@vger.kernel.org

On Sat, Apr 28, 2012 at 3:04 PM, Yuchung Cheng <ycheng@google.com> wrote:

When the cwnd reduction is done, ssthresh may be infinite if TCP enters CWR via ECN or F-RTO. If cwnd is not undone, i.e., undo_marker is set, tcp_complete_cwr() falsely set cwnd to the infinite ssthresh value. The correct operation is to keep cwnd intact because it has been updated in ECN or F-RTO.

Signed-off-by: Yuchung Cheng <ycheng@google.com>

---

 net/ipv4/tcp_input.c |    8 +++---  1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index c93b0cb..ac417de 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @ -2868,11 +2868,13 @ static inline void tcp_complete_cwr(struct sock *sk)

       /* Do not moderate cwnd if it's already undone in cwr or recovery. */        if (tp->undo_marker) { -               if (inet_csk(sk)->icsk_ca_state TCP_CA_CWR) +               if (inet_csk(sk)->icsk_ca_state TCP_CA_CWR) {                        tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);

In this TCP_CA_CWR case the patch needs to add the assignment:

    tp->snd_cwnd_stamp = tcp_time_stamp;

I know that was in earlier versions of your patch; looks like it just
got accidentally dropped on this latest version.

Otherwise, looks good to me.

neal