tcp: add CDG congestion control

CAIA Delay-Gradient (CDG) is a TCP congestion control that modifies
the TCP sender in order to [1]:

  o Use the delay gradient as a congestion signal.
  o Back off with an average probability that is independent of the RTT.
  o Coexist with flows that use loss-based congestion control, i.e.,
    flows that are unresponsive to the delay signal.
  o Tolerate packet loss unrelated to congestion. (Disabled by default.)

Its FreeBSD implementation was presented for the ICCRG in July 2012;
slides are available at http://www.ietf.org/proceedings/84/iccrg.html

Running the experiment scenarios in [1] suggests that our implementation
achieves more goodput compared with FreeBSD 10.0 senders, although it also
causes more queueing delay for a given backoff factor.

The loss tolerance heuristic is disabled by default due to safety concerns
for its use in the Internet [2, p. 45-46].

We use a variant of the Hybrid Slow start algorithm in tcp_cubic to reduce
the probability of slow start overshoot.

[1] D.A. Hayes and G. Armitage. "Revisiting TCP congestion control using
    delay gradients." In Networking 2011, pages 328-341. Springer, 2011.
[2] K.K. Jonassen. "Implementing CAIA Delay-Gradient in Linux."
    MSc thesis. Department of Informatics, University of Oslo, 2015.

Cc: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: David Hayes <davihay@ifi.uio.no>
Cc: Andreas Petlund <apetlund@simula.no>
Cc: Dave Taht <dave.taht@bufferbloat.net>
Cc: Nicolas Kuhn <nicolas.kuhn@telecom-bretagne.eu>
Signed-off-by: Kenneth Klette Jonassen <kennetkl@ifi.uio.no>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 0 deletions

diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index d83071dccd74..6fb3c90ad726 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -615,6 +615,22 @@ config TCP_CONG_DCTCP
         For further details see:
           http://simula.stanford.edu/~alizade/Site/DCTCP_files/dctcp-final.pdf
 
+config TCP_CONG_CDG
+        tristate "CAIA Delay-Gradient (CDG)"
+        default n
+        ---help---
+        CAIA Delay-Gradient (CDG) is a TCP congestion control that modifies
+        the TCP sender in order to:
+
+          o Use the delay gradient as a congestion signal.
+          o Back off with an average probability that is independent of the RTT.
+          o Coexist with flows that use loss-based congestion control.
+          o Tolerate packet loss unrelated to congestion.
+
+        For further details see:
+          D.A. Hayes and G. Armitage. "Revisiting TCP congestion control using
+          delay gradients." In Networking 2011. Preprint: http://goo.gl/No3vdg
+
 choice
         prompt "Default TCP congestion control"
         default DEFAULT_CUBIC
@@ -646,6 +662,9 @@ choice
         config DEFAULT_DCTCP
                 bool "DCTCP" if TCP_CONG_DCTCP=y
 
+        config DEFAULT_CDG
+                bool "CDG" if TCP_CONG_CDG=y
+
         config DEFAULT_RENO
                 bool "Reno"
 endchoice
@@ -668,6 +687,7 @@ config DEFAULT_TCP_CONG
         default "veno" if DEFAULT_VENO
         default "reno" if DEFAULT_RENO
         default "dctcp" if DEFAULT_DCTCP
+        default "cdg" if DEFAULT_CDG
         default "cubic"
 
 config TCP_MD5SIG