| Message ID | 1442619503-2282-1-git-send-email-bro.devel+kernel@gmail.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index d0ad355..7096b8b 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2145,6 +2145,11 @@ repair: tcp_cwnd_validate(sk, is_cwnd_limited); return false; } + /* We are prevented from transmitting because we are limited + * by the CWND, so update tcp sock with correct value. + */ + if (is_cwnd_limited) + tp->is_cwnd_limited = is_cwnd_limited; return !tp->packets_out && tcp_send_head(sk); }
Application limited streams such as thin streams, that transmit small amounts of payload in relatively few packets per RTT, are prevented from growing the CWND after experiencing loss. This leads to increased sojourn times for data segments in streams that often transmit time-dependent data. After the CWND is reduced due to loss, and an ACK has made room in the send window for more packets to be transmitted, the CWND will not grow unless there is more unsent data buffered in the output queue than the CWND permits to be sent. That is because tcp_cwnd_validate(), which updates tp->is_cwnd_limited, is only called in tcp_write_xmit() when at least one packet with new data has been sent. However, if all the buffered data in the output queue was sent within the current CWND, is_cwnd_limited will remain false even when there is no more room in the CWND. While the CWND is fully utilized, any new data put on the output queue will be held back (i.e. limited by the CWND), but tp->is_cwnd_limited will not be updated as no packets were transmitted. Fix by updating tp->is_cwnd_limited if no packets are sent due to the CWND being fully utilized. Cc: Andreas Petlund <apetlund@simula.no> Cc: Carsten Griwodz <griff@simula.no> Cc: Jonas Markussen <jonassm@ifi.uio.no> Cc: Kenneth Klette Jonassen <kennetkl@ifi.uio.no> Signed-off-by: Bendik Rønning Opstad <bro.devel+kernel@gmail.com> --- net/ipv4/tcp_output.c | 5 +++++ 1 file changed, 5 insertions(+)