linux-toradex.git/net/ipv4/tcp_bic.c, branch v3.14.50

tcp: properly handle stretch acks in slow start

2013-11-05T00:57:59+00:00

Slow start now increases cwnd by 1 if an ACK acknowledges some packets,
regardless the number of packets. Consequently slow start performance
is highly dependent on the degree of the stretch ACKs caused by
receiver or network ACK compression mechanisms (e.g., delayed-ACK,
GRO, etc).  But slow start algorithm is to send twice the amount of
packets of packets left so it should process a stretch ACK of degree
N as if N ACKs of degree 1, then exits when cwnd exceeds ssthresh. A
follow up patch will use the remainder of the N (if greater than 1)
to adjust cwnd in the congestion avoidance phase.

In addition this patch retires the experimental limited slow start
(LSS) feature. LSS has multiple drawbacks but questionable benefit. The
fractional cwnd increase in LSS requires a loop in slow start even
though it's rarely used. Configuring such an increase step via a global
sysctl on different BDPS seems hard. Finally and most importantly the
slow start overshoot concern is now better covered by the Hybrid slow
start (hystart) enabled by default.

Signed-off-by: Yuchung Cheng 
Signed-off-by: Neal Cardwell 
Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: fix undo after RTO for BIC

2012-01-20T19:17:26+00:00

This patch fixes BIC so that cwnd reductions made during RTOs can be
undone (just as they already can be undone when using the default/Reno
behavior).

When undoing cwnd reductions, BIC-derived congestion control modules
were restoring the cwnd from last_max_cwnd. There were two problems
with using last_max_cwnd to restore a cwnd during undo:

(a) last_max_cwnd was set to 0 on state transitions into TCP_CA_Loss
(by calling the module's reset() functions), so cwnd reductions from
RTOs could not be undone.

(b) when fast_covergence is enabled (which it is by default)
last_max_cwnd does not actually hold the value of snd_cwnd before the
loss; instead, it holds a scaled-down version of snd_cwnd.

This patch makes the following changes:

(1) upon undo, revert snd_cwnd to ca->loss_cwnd, which is already, as
the existing comment notes, the "congestion window at last loss"

(2) stop forgetting ca->loss_cwnd on TCP_CA_Loss events

(3) use ca->last_max_cwnd to check if we're in slow start

Signed-off-by: Neal Cardwell 
Signed-off-by: David S. Miller

tcp: mark tcp_congestion_ops read_mostly

2011-03-10T08:40:17+00:00

Signed-off-by: Stephen Hemminger 
Signed-off-by: David S. Miller

tcp: add helper for AI algorithm

2009-03-02T11:00:15+00:00

It seems that implementation in yeah was inconsistent to what
other did as it would increase cwnd one ack earlier than the
others do.

Size benefits:

  bictcp_cong_avoid |  -36
  tcp_cong_avoid_ai |  +52
  bictcp_cong_avoid |  -34
  tcp_scalable_cong_avoid |  -36
  tcp_veno_cong_avoid |  -12
  tcp_yeah_cong_avoid |  -38

= -104 bytes total

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller

[TCP]: BIC web page link is corrected.

2008-02-29T06:14:32+00:00

Signed-off-by: Sangtae Ha 
Signed-off-by: David S. Miller

[TCP]: Cong.ctrl modules: remove unused good_ack from cong_avoid

2008-01-28T22:55:41+00:00

Signed-off-by: Ilpo Järvinen 
Signed-off-by: Herbert Xu 
Signed-off-by: David S. Miller

[TCP]: Remove num_acked>0 checks from cong.ctrl mods pkts_acked

2007-10-10T23:47:55+00:00

There is no need for such check in pkts_acked because the
callback is not invoked unless at least one segment got fully
ACKed (i.e., the snd_una moved past skb's end_seq) by the
cumulative ACK's snd_una advancement.

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller

[TCP]: congestion control API pass RTT in microseconds

2007-07-31T09:27:57+00:00

This patch changes the API for the callback that is done after an ACK is
received. It solves a couple of issues:

  * Some congestion controls want higher resolution value of RTT
    (controlled by TCP_CONG_RTT_SAMPLE flag). These don't really want a ktime, but
    all compute a RTT in microseconds.

  * Other congestion control could use RTT at jiffies resolution.

To keep API consistent the units should be the same for both cases, just the
resolution should change.

Signed-off-by: Stephen Hemminger 
Signed-off-by: David S. Miller

[TCP]: remove unused argument to cong_avoid op

2007-07-18T08:46:58+00:00

None of the existing TCP congestion controls use the rtt value pased
in the ca_ops->cong_avoid interface.  Which is lucky because seq_rtt
could have been -1 when handling a duplicate ack.

Signed-off-by: Stephen Hemminger 
Signed-off-by: David S. Miller

[TCP]: Set initial_ssthresh default to zero in Cubic and BIC.

2007-06-13T08:03:53+00:00

Because of the current default of 100, Cubic and BIC perform very
poorly compared to standard Reno.

In the worst case, this change makes Cubic and BIC as aggressive as
Reno.  So this change should be very safe.

Signed-off-by: David S. Miller