[TCP] CUBIC v2.3

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

1 files changed, 109 insertions, 11 deletions

diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 4a1221e5e8e..ee467ec40c4 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -1,13 +1,23 @@
 /*
- * TCP CUBIC: Binary Increase Congestion control for TCP v2.2
+ * TCP CUBIC: Binary Increase Congestion control for TCP v2.3
  * 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
+ * Sangtae Ha, Injong Rhee and Lisong Xu,
+ *  "CUBIC: A New TCP-Friendly High-Speed TCP Variant"
+ *  in ACM SIGOPS Operating System Review, July 2008.
  * Available from:
- *  http://netsrv.csc.ncsu.edu/export/cubic-paper.pdf
+ *  http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf
+ *
+ * CUBIC integrates a new slow start algorithm, called HyStart.
+ * The details of HyStart are presented in
+ *  Sangtae Ha and Injong Rhee,
+ *  "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008.
+ * Available from:
+ *  http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf
+ *
+ * All testing results are available from:
+ * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing
  *
  * Unless CUBIC is enabled and congestion window is large
  * this behaves the same as the original Reno.
@@ -23,12 +33,26 @@
                                          */
 #define BICTCP_HZ               10      /* BIC HZ 2^10 = 1024 */
 
+/* Two methods of hybrid slow start */
+#define HYSTART_ACK_TRAIN       0x1
+#define HYSTART_DELAY           0x2
+
+/* Number of delay samples for detecting the increase of delay */
+#define HYSTART_MIN_SAMPLES     8
+#define HYSTART_DELAY_MIN       (2U<<3)
+#define HYSTART_DELAY_MAX       (16U<<3)
+#define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)
+
 static int fast_convergence __read_mostly = 1;
 static int beta __read_mostly = 717;    /* = 717/1024 (BICTCP_BETA_SCALE) */
 static int initial_ssthresh __read_mostly;
 static int bic_scale __read_mostly = 41;
 static int tcp_friendliness __read_mostly = 1;
 
+static int hystart __read_mostly = 1;
+static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;
+static int hystart_low_window __read_mostly = 16;
+
 static u32 cube_rtt_scale __read_mostly;
 static u32 beta_scale __read_mostly;
 static u64 cube_factor __read_mostly;
@@ -44,6 +68,13 @@ module_param(bic_scale, int, 0444);
 MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
 module_param(tcp_friendliness, int, 0644);
 MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
+module_param(hystart, int, 0644);
+MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm");
+module_param(hystart_detect, int, 0644);
+MODULE_PARM_DESC(hystart_detect, "hyrbrid slow start detection mechanisms"
+                 " 1: packet-train 2: delay 3: both packet-train and delay");
+module_param(hystart_low_window, int, 0644);
+MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start");
 
 /* BIC TCP Parameters */
 struct bictcp {
@@ -59,7 +90,13 @@ struct bictcp {
         u32     ack_cnt;        /* number of acks */
         u32     tcp_cwnd;       /* estimated tcp cwnd */
 #define ACK_RATIO_SHIFT 4
-        u32     delayed_ack;    /* estimate the ratio of Packets/ACKs << 4 */
+        u16     delayed_ack;    /* estimate the ratio of Packets/ACKs << 4 */
+        u8      sample_cnt;     /* number of samples to decide curr_rtt */
+        u8      found;          /* the exit point is found? */
+        u32     round_start;    /* beginning of each round */
+        u32     end_seq;        /* end_seq of the round */
+        u32     last_jiffies;   /* last time when the ACK spacing is close */
+        u32     curr_rtt;       /* the minimum rtt of current round */
 };
 
 static inline void bictcp_reset(struct bictcp *ca)
@@ -76,12 +113,28 @@ static inline void bictcp_reset(struct bictcp *ca)
         ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
         ca->ack_cnt = 0;
         ca->tcp_cwnd = 0;
+        ca->found = 0;
+}
+
+static inline void bictcp_hystart_reset(struct sock *sk)
+{
+        struct tcp_sock *tp = tcp_sk(sk);
+        struct bictcp *ca = inet_csk_ca(sk);
+
+        ca->round_start = ca->last_jiffies = jiffies;
+        ca->end_seq = tp->snd_nxt;
+        ca->curr_rtt = 0;
+        ca->sample_cnt = 0;
 }
 
 static void bictcp_init(struct sock *sk)
 {
         bictcp_reset(inet_csk_ca(sk));
-        if (initial_ssthresh)
+
+        if (hystart)
+                bictcp_hystart_reset(sk);
+
+        if (!hystart && initial_ssthresh)
                 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
 }
 
@@ -235,9 +288,11 @@ static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
         if (!tcp_is_cwnd_limited(sk, in_flight))
                 return;
 
-        if (tp->snd_cwnd <= tp->snd_ssthresh)
+        if (tp->snd_cwnd <= tp->snd_ssthresh) {
+                if (hystart && after(ack, ca->end_seq))
+                        bictcp_hystart_reset(sk);
                 tcp_slow_start(tp);
-        else {
+        } else {
                 bictcp_update(ca, tp->snd_cwnd);
 
                 /* In dangerous area, increase slowly.
@@ -281,8 +336,45 @@ static u32 bictcp_undo_cwnd(struct sock *sk)
 
 static void bictcp_state(struct sock *sk, u8 new_state)
 {
-        if (new_state == TCP_CA_Loss)
+        if (new_state == TCP_CA_Loss) {
                 bictcp_reset(inet_csk_ca(sk));
+                bictcp_hystart_reset(sk);
+        }
+}
+
+static void hystart_update(struct sock *sk, u32 delay)
+{
+        struct tcp_sock *tp = tcp_sk(sk);
+        struct bictcp *ca = inet_csk_ca(sk);
+
+        if (!(ca->found & hystart_detect)) {
+                u32 curr_jiffies = jiffies;
+
+                /* first detection parameter - ack-train detection */
+                if (curr_jiffies - ca->last_jiffies <= msecs_to_jiffies(2)) {
+                        ca->last_jiffies = curr_jiffies;
+                        if (curr_jiffies - ca->round_start >= ca->delay_min>>4)
+                                ca->found |= HYSTART_ACK_TRAIN;
+                }
+
+                /* obtain the minimum delay of more than sampling packets */
+                if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
+                        if (ca->curr_rtt == 0 || ca->curr_rtt > delay)
+                                ca->curr_rtt = delay;
+
+                        ca->sample_cnt++;
+                } else {
+                        if (ca->curr_rtt > ca->delay_min +
+                            HYSTART_DELAY_THRESH(ca->delay_min>>4))
+                                ca->found |= HYSTART_DELAY;
+                }
+                /*
+                 * Either one of two conditions are met,
+                 * we exit from slow start immediately.
+                 */
+                if (ca->found & hystart_detect)
+                        tp->snd_ssthresh = tp->snd_cwnd;
+        }
 }
 
 /* Track delayed acknowledgment ratio using sliding window
@@ -291,6 +383,7 @@ static void bictcp_state(struct sock *sk, u8 new_state)
 static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
 {
         const struct inet_connection_sock *icsk = inet_csk(sk);
+        const struct tcp_sock *tp = tcp_sk(sk);
         struct bictcp *ca = inet_csk_ca(sk);
         u32 delay;
 
@@ -314,6 +407,11 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
         /* first time call or link delay decreases */
         if (ca->delay_min == 0 || ca->delay_min > delay)
                 ca->delay_min = delay;
+
+        /* hystart triggers when cwnd is larger than some threshold */
+        if (hystart && tp->snd_cwnd <= tp->snd_ssthresh &&
+            tp->snd_cwnd >= hystart_low_window)
+                hystart_update(sk, delay);
 }
 
 static struct tcp_congestion_ops cubictcp = {
@@ -372,4 +470,4 @@ module_exit(cubictcp_unregister);
 MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("CUBIC TCP");
-MODULE_VERSION("2.2");
+MODULE_VERSION("2.3");