From: Thomas Graf <tgraf@redhat.com>
Date: Fri, 23 Jul 2010 15:34:13 -0400
Subject: [net] tcp: TCP cubic v2.2
Message-id: <20100723153413.GI14925@lsx.localdomain>
Patchwork-id: 27067
O-Subject: [RHEL5.6 PATCH 7/14] tcp: TCP cubic v2.2
Bugzilla: 612709
RH-Acked-by: Neil Horman <nhorman@redhat.com>
RH-Acked-by: David S. Miller <davem@redhat.com>

The change removes the module parameter max_increment. Is this ok?
Or should we leave the option around and simply ignore it in order
not to break anything?

commit 6b3d626321c1d4ce9138a86b047dfafc6a403016
Author: Sangtae Ha <sha2@ncsu.edu>
Date:   Tue Mar 4 14:17:41 2008 -0800

    [TCP]: TCP cubic v2.2

    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-2.6.23.9

    Signed-off-by: Sangtae Ha <sha2@ncsu.edu>
    Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Jarod Wilson <jarod@redhat.com>

diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index e625d7b..f877793 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -1,12 +1,13 @@
 /*
- * TCP CUBIC: Binary Increase Congestion control for TCP v2.1
- *
+ * TCP CUBIC: Binary Increase Congestion control for TCP v2.2
+ * Home page:
+ *      http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
  * This is from the implementation of CUBIC TCP in
  * Injong Rhee, Lisong Xu.
  *  "CUBIC: A New TCP-Friendly High-Speed TCP Variant
  *  in PFLDnet 2005
  * Available from:
- *  http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf
+ *  http://netsrv.csc.ncsu.edu/export/cubic-paper.pdf
  *
  * Unless CUBIC is enabled and congestion window is large
  * this behaves the same as the original Reno.
@@ -20,15 +21,10 @@
 #define BICTCP_BETA_SCALE    1024	/* Scale factor beta calculation
 					 * max_cwnd = snd_cwnd * beta
 					 */
-#define BICTCP_B		4	 /*
-					  * In binary search,
-					  * go to point (max+min)/N
-					  */
 #define	BICTCP_HZ		10	/* BIC HZ 2^10 = 1024 */
 
 static int fast_convergence = 1;
-static int max_increment = 16;
-static int beta = 819;		/* = 819/1024 (BICTCP_BETA_SCALE) */
+static int beta __read_mostly = 717;	/* = 717/1024 (BICTCP_BETA_SCALE) */
 static int initial_ssthresh;
 static int bic_scale = 41;
 static int tcp_friendliness = 1;
@@ -40,9 +36,7 @@ static u64 cube_factor;
 /* Note parameters that are used for precomputing scale factors are read-only */
 module_param(fast_convergence, int, 0644);
 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
-module_param(max_increment, int, 0644);
-MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
-module_param(beta, int, 0444);
+module_param(beta, int, 0644);
 MODULE_PARM_DESC(beta, "beta for multiplicative increase");
 module_param(initial_ssthresh, int, 0644);
 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
@@ -169,7 +163,7 @@ static u32 cubic_root(u64 a)
 static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
 {
 	u64 offs;
-	u32 delta, t, bic_target, min_cnt, max_cnt;
+	u32 delta, t, bic_target, max_cnt;
 
 	ca->ack_cnt++;	/* count the number of ACKs */
 
@@ -235,19 +229,6 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
                 ca->cnt = 100 * cwnd;              /* very small increment*/
         }
 
-	if (ca->delay_min > 0) {
-		/* max increment = Smax * rtt / 0.1  */
-		min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);
-
-		/* use concave growth when the target is above the origin */
-		if (ca->cnt < min_cnt && t >= ca->bic_K)
-			ca->cnt = min_cnt;
-	}
-
-        /* slow start and low utilization  */
-	if (ca->loss_cwnd == 0)		/* could be aggressive in slow start */
-		ca->cnt = 50;
-
 	/* TCP Friendly */
 	if (tcp_friendliness) {
 		u32 scale = beta_scale;
@@ -426,4 +407,4 @@ module_exit(cubictcp_unregister);
 MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("CUBIC TCP");
-MODULE_VERSION("2.1");
+MODULE_VERSION("2.2");