We have updated CUBIC to fix some issues with slow increase in large
BDP networks. We also improved its convergence speed. The fix is in
fact very simple -- the window increase limit of smax during the
window probing phase (i.e., convex growth phase) is removed. We found
that this does not affect TCP friendliness, but only improves its
scalability. We have run some tests in our lab and also over the
Internet path from NCSU to Japan. These results can be seen from the
following page:

http://netsrv.csc.ncsu.edu/wiki/index.php/Intra_protocol_fairness_testing_with_linux-2.6.23.9
http://netsrv.csc.ncsu.edu/wiki/index.php/RTT_fairness_testing_with_linux-2.6.23.9
http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_friendliness_testing_with_linux-2.6.23.9Signed-off-by: NSangtae Ha <sha2@ncsu.edu>
Signed-off-by: NStephen Hemminger <shemminger@vyatta.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

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: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Remove use of received timestamp option value from RTT calculation in Cubic.
A hostile receiver may be returning a larger timestamp option than the original
value. This would cause the sender to believe the malevolent receiver had
a larger RTT and because Cubic tries to provide some RTT friendliness, the
sender would then favor the liar.

Instead, use the jiffie resolutionRTT value already computed and
passed back after ack.
Signed-off-by: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

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: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

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: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

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: NDavid S. Miller <davem@davemloft.net>

Do some simple changes to make congestion control API faster/cleaner.
* use ktime_t rather than timeval
* merge rtt sampling into existing ack callback
  this means one indirect call versus two per ack.
* use flags bits to store options/settings
Signed-off-by: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The following update received from Injong updates TCP cubic to the latest
version. I am running more complete tests and will have results after 4/1.

According to Injong: the new version improves on its scalability,
fairness and stability.  So in all properties, we confirmed it shows better
performance.

NCSU results (for 2.6.18 and 2.6.20) available:
	http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing

This version is described in a new Internet draft for CUBIC.
	http://www.ietf.org/internet-drafts/draft-rhee-tcp-cubic-00.txtSigned-off-by: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Use willy's work in optimizing cube root by having table for small values.
Signed-off-by: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The Newton-Raphson method is quadratically convergent so
only a small fixed number of steps are necessary.
Therefore it is faster to unroll the loop. Since div64_64 is no longer
inline it won't cause code explosion.

Also fixes a bug that can occur if x^2 was bigger than 32 bits.
Signed-off-by: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Here is the current version of the 64 bit divide common code.
Signed-off-by: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

These module parameters should be in the read mostly area to avoid
cache pollution.
Signed-off-by: NStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Doug Leith observed a discrepancy between the version of CUBIC described
in the papers and the version in 2.6.18. A math error related to scaling
causes Cubic to grow too slowly.

Patch is from "Sangtae Ha" <sha2@ncsu.edu>. I validated that
it does fix the problems.

See the following to show behavior over 500ms 100 Mbit link.

Sender (2.6.19-rc3) ---  Bridge (2.6.18-rt7) ------- Receiver (2.6.19-rc3)
                    1G      [netem]           100M

	http://developer.osdl.org/shemminger/tcp/2.6.19-rc3/cubic-orig.png
	http://developer.osdl.org/shemminger/tcp/2.6.19-rc3/cubic-fix.pngSigned-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NJörn Engel <joern@wohnheim.fh-wedel.de>
Signed-off-by: NAdrian Bunk <bunk@stusta.de>

Many of the TCP congestion methods all just use ssthresh
as the minimum congestion window on decrease.  Rather than
duplicating the code, just have that be the default if that
handle in the ops structure is not set.

Minor behaviour change to TCP compound.  It probably wants
to use this (ssthresh) as lower bound, rather than ssthresh/2
because the latter causes undershoot on loss.
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Replace cube root algorithim with a faster version using Newton-Raphson.
Surprisingly, doing the scaled div64_64 is faster than a true 64 bit
division on 64 bit CPU's.
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Revised version of patch to pre-compute values for TCP cubic.
  * d32,d64 replaced with descriptive names
  * cube_factor replaces
	 srtt[scaled by count] / HZ * ((1 << (10+2*BICTCP_HZ)) / bic_scale)
  * beta_scale replaces
	8*(BICTCP_BETA_SCALE+beta)/3/(BICTCP_BETA_SCALE-beta);
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Replace existing BIC version 1.1 with new version 2.0.
The main change is to replace the window growth function
with a cubic function as described in:
  http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdfSigned-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>