| Message ID | 1418327890-368-1-git-send-email-sebastien.barre@uclouvain.be |
|---|---|
| State | Deferred, archived |
| Delegated to: | David Miller |
| Headers | show |
The net-next tree is closed, therefore it is not appropriate to submit net-next changes at this time. Thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Le 11/12/2014 21:14, David Miller a écrit : > The net-next tree is closed, therefore it is not appropriate to submit net-next > changes at this time. Sorry for that, I missed your mail announcing that next-next was closed. Will resubmit when it is open again. regards, Sébastien. > > Thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, Dec 11, 2014 at 2:58 PM, Sébastien Barré <sebastien.barre@uclouvain.be> wrote: > When the peer has delayed ack enabled, it may reply to a probe with an > ACK+D-SACK, with ack value set to tlp_high_seq. In the current code, > such ACK+DSACK will be missed and only at next, higher ack will the TLP > episode be considered done. Since the DSACK is not present anymore, > this will cost a cwnd reduction. > > This patch ensures that this scenario does not cause a cwnd reduction, since > receiving an ACK+DSACK indicates that both the initial segment and the probe > have been received by the peer. > > Cc: Gregory Detal <gregory.detal@uclouvain.be> > Cc: Nandita Dukkipati <nanditad@google.com> > Cc: Yuchung Cheng <ycheng@google.com> > Signed-off-by: Sébastien Barré <sebastien.barre@uclouvain.be> BTW, I like this idea, and I'll test it. Two suggestions for the next iteration: (1) for TCP patch style, I'd suggest a commit first-line like: tcp: avoid reducing cwnd when ACK+DSACK is received (2) Your patch is essentially a reworking of the is_tlp_dupack computation. So rather than splitting the logic between the is_tlp_dupack computation and the new expression inside the if condition, I'd suggest moving and centralizing all the logic in the if condition. There is no real need for the is_tlp_dupack variable. neal -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 075ab4d..fb007cc 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -3369,23 +3369,23 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag) /* Mark the end of TLP episode on receiving TLP dupack or when * ack is after tlp_high_seq. + * With delayed acks, we may also get a regular ACK+DSACK, in which + * case we don't want to reduce the cwnd either. */ - if (is_tlp_dupack) { + if (is_tlp_dupack || + !before(ack, tp->tlp_high_seq) && (flag & FLAG_DSACKING_ACK)) { tp->tlp_high_seq = 0; return; } if (after(ack, tp->tlp_high_seq)) { tp->tlp_high_seq = 0; - /* Don't reduce cwnd if DSACK arrives for TLP retrans. */ - if (!(flag & FLAG_DSACKING_ACK)) { - tcp_init_cwnd_reduction(sk); - tcp_set_ca_state(sk, TCP_CA_CWR); - tcp_end_cwnd_reduction(sk); - tcp_try_keep_open(sk); - NET_INC_STATS_BH(sock_net(sk), - LINUX_MIB_TCPLOSSPROBERECOVERY); - } + tcp_init_cwnd_reduction(sk); + tcp_set_ca_state(sk, TCP_CA_CWR); + tcp_end_cwnd_reduction(sk); + tcp_try_keep_open(sk); + NET_INC_STATS_BH(sock_net(sk), + LINUX_MIB_TCPLOSSPROBERECOVERY); } }
When the peer has delayed ack enabled, it may reply to a probe with an ACK+D-SACK, with ack value set to tlp_high_seq. In the current code, such ACK+DSACK will be missed and only at next, higher ack will the TLP episode be considered done. Since the DSACK is not present anymore, this will cost a cwnd reduction. This patch ensures that this scenario does not cause a cwnd reduction, since receiving an ACK+DSACK indicates that both the initial segment and the probe have been received by the peer. Cc: Gregory Detal <gregory.detal@uclouvain.be> Cc: Nandita Dukkipati <nanditad@google.com> Cc: Yuchung Cheng <ycheng@google.com> Signed-off-by: Sébastien Barré <sebastien.barre@uclouvain.be> --- net/ipv4/tcp_input.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-)