On Wed, 2015-09-23 at 18:49 +0200, Bendik Rønning Opstad wrote:
> Application limited streams such as thin streams, that transmit small
> amounts of payload in relatively few packets per RTT, can be prevented
> from growing the CWND when in congestion avoidance. This leads to
> increased sojourn times for data segments in streams that often transmit
> time-dependent data.
>
> Currently, a connection is considered CWND limited only after having
> successfully transmitted at least one packet with new data, while at the
> same time failing to transmit some unsent data from the output queue
> because the CWND is full. Applications that produce small amounts of
> data may be left in a state where it is never considered to be CWND
> limited, because all unsent data is successfully transmitted each time
> an incoming ACK opens up for more data to be transmitted in the send
> window.
>
> Fix by always testing whether the CWND is fully used after successful
> packet transmissions, such that a connection is considered CWND limited
> whenever the CWND has been filled. This is the correct behavior as
> specified in RFC2861 (section 3.1).
>
> Cc: Andreas Petlund <apetl...@simula.no>
> Cc: Carsten Griwodz <gr...@simula.no>
> Cc: Jonas Markussen <jona...@ifi.uio.no>
> Cc: Kenneth Klette Jonassen <kenne...@ifi.uio.no>
> Cc: Mads Johannessen <mads...@ifi.uio.no>
> Signed-off-by: Bendik Rønning Opstad <bro.devel+ker...@gmail.com>
> ---
> Changes in v2:
> - Instead of updating tp->is_cwnd_limited after failing to send
> any packets, test whether CWND is full after successfull packet
> transmissions.
> - Updating commit message according to changes.
>
> net/ipv4/tcp_output.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 4cd0b50..57a586f 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -1827,7 +1827,7 @@ static bool tcp_tso_should_defer(struct sock *sk,
> struct sk_buff *skb,
>
> /* Ok, it looks like it is advisable to defer. */
>
> - if (cong_win < send_win && cong_win < skb->len)
> + if (cong_win < send_win && cong_win <= skb->len)
> *is_cwnd_limited = true;
>
> return true;
> @@ -2060,7 +2060,6 @@ static bool tcp_write_xmit(struct sock *sk, unsigned
> int mss_now, int nonagle,
>
> cwnd_quota = tcp_cwnd_test(tp, skb);
> if (!cwnd_quota) {
> - is_cwnd_limited = true;
> if (push_one == 2)
> /* Force out a loss probe pkt. */
> cwnd_quota = 1;
> @@ -2142,6 +2141,7 @@ repair:
> /* Send one loss probe per tail loss episode. */
> if (push_one != 2)
> tcp_schedule_loss_probe(sk);
> + is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
> tcp_cwnd_validate(sk, is_cwnd_limited);
> return false;
> }
David, any idea of what happened to Bendik patch ?
https://patchwork.ozlabs.org/patch/521765
Do we need to re-submit or something ?
Thanks !
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