diff options
author | Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> | 2007-03-02 13:34:19 -0800 |
---|---|---|
committer | David S. Miller <davem@sunset.davemloft.net> | 2007-04-25 22:23:26 -0700 |
commit | e317f6f69cb95527799d308a9421b7dc1252989a (patch) | |
tree | 141ff608a450f1d768383f300cc204db5904b20c /net/ipv4/tcp_input.c | |
parent | e01f9d7793be82e6c252efbd52c399d3eb65abe4 (diff) |
[TCP]: FRTO undo response falls back to ratehalving one if ECEd
Undoing ssthresh is disabled in fastretrans_alert whenever
FLAG_ECE is set by clearing prior_ssthresh. The clearing does
not protect FRTO because FRTO operates before fastretrans_alert.
Moving the clearing of prior_ssthresh earlier seems to be a
suboptimal solution to the FRTO case because then FLAG_ECE will
cause a second ssthresh reduction in try_to_open (the first
occurred when FRTO was entered). So instead, FRTO falls back
immediately to the rate halving response, which switches TCP to
CA_CWR state preventing the latter reduction of ssthresh.
If the first ECE arrived before the ACK after which FRTO is able
to decide RTO as spurious, prior_ssthresh is already cleared.
Thus no undoing for ssthresh occurs. Besides, FLAG_ECE should be
set also in the following ACKs resulting in rate halving response
that sees TCP is already in CA_CWR, which again prevents an extra
ssthresh reduction on that round-trip.
If the first ECE arrived before RTO, ssthresh has already been
adapted and prior_ssthresh remains cleared on entry because TCP
is in CA_CWR (the same applies also to a case where FRTO is
entered more than once and ECE comes in the middle).
High_seq must not be touched after tcp_enter_cwr because CWR
round-trip calculation depends on it.
I believe that after this patch, FRTO should be ECN-safe and
even able to take advantage of synergy benefits.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_input.c')
-rw-r--r-- | net/ipv4/tcp_input.c | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index cb715eadf8f..d894bbcc1d2 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -2587,14 +2587,15 @@ static void tcp_conservative_spur_to_response(struct tcp_sock *tp) */ static void tcp_ratehalving_spur_to_response(struct sock *sk) { - struct tcp_sock *tp = tcp_sk(sk); tcp_enter_cwr(sk, 0); - tp->high_seq = tp->frto_highmark; /* Smoother w/o this? - ij */ } -static void tcp_undo_spur_to_response(struct sock *sk) +static void tcp_undo_spur_to_response(struct sock *sk, int flag) { - tcp_undo_cwr(sk, 1); + if (flag&FLAG_ECE) + tcp_ratehalving_spur_to_response(sk); + else + tcp_undo_cwr(sk, 1); } /* F-RTO spurious RTO detection algorithm (RFC4138) @@ -2681,7 +2682,7 @@ static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag) } else /* frto_counter == 2 */ { switch (sysctl_tcp_frto_response) { case 2: - tcp_undo_spur_to_response(sk); + tcp_undo_spur_to_response(sk, flag); break; case 1: tcp_conservative_spur_to_response(tp); |