[TCP]: TCP Illinois update.

This version more closely matches the paper, and fixes several
math errors. The biggest difference is that it updates alpha/beta
once per RTT

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

1 files changed, 186 insertions, 112 deletions

diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c
index 91a2a34604cd..ae6298600886 100644
--- a/net/ipv4/tcp_illinois.c
+++ b/net/ipv4/tcp_illinois.c
@@ -23,74 +23,106 @@
 #define ALPHA_MIN       ((3*ALPHA_SCALE)/10)    /* ~0.3 */
 #define ALPHA_MAX       (10*ALPHA_SCALE)        /* 10.0 */
 #define ALPHA_BASE      ALPHA_SCALE             /* 1.0 */
+#define U32_MAX         ((u32)~0U)
+#define RTT_MAX         (U32_MAX / ALPHA_MAX)   /* 3.3 secs */
 
 #define BETA_SHIFT      6
 #define BETA_SCALE      (1u<<BETA_SHIFT)
-#define BETA_MIN        (BETA_SCALE/8)          /* 0.8 */
-#define BETA_MAX        (BETA_SCALE/2)
-#define BETA_BASE       BETA_MAX                /* 0.5 */
-
-#define THETA           5
+#define BETA_MIN        (BETA_SCALE/8)          /* 0.125 */
+#define BETA_MAX        (BETA_SCALE/2)          /* 0.5 */
+#define BETA_BASE       BETA_MAX
 
 static int win_thresh __read_mostly = 15;
-module_param(win_thresh, int, 0644);
+module_param(win_thresh, int, 0);
 MODULE_PARM_DESC(win_thresh, "Window threshold for starting adaptive sizing");
 
-#define MAX_RTT         0x7fffffff
+static int theta __read_mostly = 5;
+module_param(theta, int, 0);
+MODULE_PARM_DESC(theta, "# of fast RTT's before full growth");
 
 /* TCP Illinois Parameters */
-struct tcp_illinois {
-        u32     last_alpha;
-        u32     min_rtt;
-        u32     max_rtt;
-        u32     rtt_low;
-        u32     rtt_cnt;
-        u64     sum_rtt;
+struct illinois {
+        u64     sum_rtt;        /* sum of rtt's measured within last rtt */
+        u16     cnt_rtt;        /* # of rtts measured within last rtt */
+        u32     base_rtt;       /* min of all rtt in usec */
+        u32     max_rtt;        /* max of all rtt in usec */
+        u32     end_seq;        /* right edge of current RTT */
+        u32     alpha;          /* Additive increase */
+        u32     beta;           /* Muliplicative decrease */
+        u16     acked;          /* # packets acked by current ACK */
+        u8      rtt_above;      /* average rtt has gone above threshold */
+        u8      rtt_low;        /* # of rtts measurements below threshold */
 };
 
+static void rtt_reset(struct sock *sk)
+{
+        struct tcp_sock *tp = tcp_sk(sk);
+        struct illinois *ca = inet_csk_ca(sk);
+
+        ca->end_seq = tp->snd_nxt;
+        ca->cnt_rtt = 0;
+        ca->sum_rtt = 0;
+
+        /* TODO: age max_rtt? */
+}
+
 static void tcp_illinois_init(struct sock *sk)
 {
-        struct tcp_illinois *ca = inet_csk_ca(sk);
+        struct illinois *ca = inet_csk_ca(sk);
+
+        ca->alpha = ALPHA_MAX;
+        ca->beta = BETA_BASE;
+        ca->base_rtt = 0x7fffffff;
+        ca->max_rtt = 0;
+
+        ca->acked = 0;
+        ca->rtt_low = 0;
+        ca->rtt_above = 0;
 
-        ca->last_alpha = ALPHA_BASE;
-        ca->min_rtt = 0x7fffffff;
+        rtt_reset(sk);
 }
 
-/*
- * Keep track of min, max and average RTT
- */
-static void tcp_illinois_rtt_calc(struct sock *sk, u32 rtt)
+/* Measure RTT for each ack. */
+static void tcp_illinois_rtt_sample(struct sock *sk, u32 rtt)
 {
-        struct tcp_illinois *ca = inet_csk_ca(sk);
+        struct illinois *ca = inet_csk_ca(sk);
+
+        /* ignore bogus values, this prevents wraparound in alpha math */
+        if (rtt > RTT_MAX)
+                rtt = RTT_MAX;
 
-        if (rtt < ca->min_rtt)
-                ca->min_rtt = rtt;
-        if (rtt > ca->max_rtt)
+        /* keep track of minimum RTT seen so far */
+        if (ca->base_rtt > rtt)
+                ca->base_rtt = rtt;
+
+        /* and max */
+        if (ca->max_rtt < rtt)
                 ca->max_rtt = rtt;
 
-        if (++ca->rtt_cnt == 1)
-                ca->sum_rtt = rtt;
-        else
-                ca->sum_rtt += rtt;
+        ++ca->cnt_rtt;
+        ca->sum_rtt += rtt;
 }
 
-/* max queuing delay */
-static inline u32 max_delay(const struct tcp_illinois *ca)
+/* Capture count of packets covered by ack, to adjust for delayed acks */
+static void tcp_illinois_acked(struct sock *sk, u32 pkts_acked)
 {
-        return ca->max_rtt - ca->min_rtt;
+        struct illinois *ca = inet_csk_ca(sk);
+        ca->acked = pkts_acked;
 }
 
-/* average queueing delay */
-static u32 avg_delay(struct tcp_illinois *ca)
+/* Maximum queuing delay */
+static inline u32 max_delay(const struct illinois *ca)
 {
-        u64 avg_rtt = ca->sum_rtt;
-
-        do_div(avg_rtt, ca->rtt_cnt);
+        return ca->max_rtt - ca->base_rtt;
+}
 
-        ca->sum_rtt = 0;
-        ca->rtt_cnt = 0;
+/* Average queuing delay */
+static inline u32 avg_delay(const struct illinois *ca)
+{
+        u64 t = ca->sum_rtt;
 
-        return avg_rtt - ca->min_rtt;
+        do_div(t, ca->cnt_rtt);
+        return t - ca->base_rtt;
 }
 
 /*
@@ -101,32 +133,31 @@ static u32 avg_delay(struct tcp_illinois *ca)
  * A. If average delay is at minimum (we are uncongested),
  *    then use large alpha (10.0) to increase faster.
  * B. If average delay is at maximum (getting congested)
- *    then use small alpha (1.0)
+ *    then use small alpha (0.3)
  *
  * The result is a convex window growth curve.
  */
-static u32 alpha(const struct sock *sk)
+static u32 alpha(struct illinois *ca, u32 da, u32 dm)
 {
-        struct tcp_sock *tp = tcp_sk(sk);
-        struct tcp_illinois *ca = inet_csk_ca(sk);
-        u32 dm = max_delay(ca);
-        u32 da = avg_delay(ca);
-        u32 d1, a;
+        u32 d1 = dm / 100;      /* Low threshold */
 
-        if (tp->snd_cwnd < win_thresh)
-                return ALPHA_BASE;      /* same as Reno (1.0) */
-
-        d1 = dm / 100;
         if (da <= d1) {
-                /* Don't let noise force agressive response */
-                if (ca->rtt_low < THETA) {
-                        ++ca->rtt_low;
-                        return ca->last_alpha;
-                } else
+                /* If never got out of low delay zone, then use max */
+                if (!ca->rtt_above)
                         return ALPHA_MAX;
+
+                /* Wait for 5 good RTT's before allowing alpha to go alpha max.
+                 * This prevents one good RTT from causing sudden window increase.
+                 */
+                if (++ca->rtt_low < theta)
+                        return ca->alpha;
+
+                ca->rtt_low = 0;
+                ca->rtt_above = 0;
+                return ALPHA_MAX;
         }
 
-        ca->rtt_low = 0;
+        ca->rtt_above = 1;
 
         /*
          * Based on:
@@ -146,37 +177,8 @@ static u32 alpha(const struct sock *sk)
 
         dm -= d1;
         da -= d1;
-
-        a = (dm * ALPHA_MAX) / (dm - (da  * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
-        ca->last_alpha = a;
-        return a;
-}
-
-/*
- * Increase window in response to successful acknowledgment.
- */
-static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
-                                    u32 in_flight, int flag)
-{
-        struct tcp_sock *tp = tcp_sk(sk);
-
-        /* RFC2861 only increase cwnd if fully utilized */
-        if (!tcp_is_cwnd_limited(sk, in_flight))
-                return;
-
-        /* In slow start */
-        if (tp->snd_cwnd <= tp->snd_ssthresh)
-                tcp_slow_start(tp);
-
-        else {
-                /* additive increase  cwnd += alpha / cwnd */
-                if ((tp->snd_cwnd_cnt * alpha(sk)) >> ALPHA_SHIFT >= tp->snd_cwnd) {
-                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-                                tp->snd_cwnd++;
-                        tp->snd_cwnd_cnt = 0;
-                } else
-                        tp->snd_cwnd_cnt++;
-        }
+        return (dm * ALPHA_MAX) /
+                (dm + (da  * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
 }
 
 /*
@@ -187,20 +189,14 @@ static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
  * If delay is up to 80% of max then beta = 1/2
  * In between is a linear function
  */
-static inline u32 beta(struct sock *sk)
+static u32 beta(u32 da, u32 dm)
 {
-        struct tcp_sock *tp = tcp_sk(sk);
-        struct tcp_illinois *ca = inet_csk_ca(sk);
-        u32 dm = max_delay(ca);
-        u32 da = avg_delay(ca);
         u32 d2, d3;
 
-        if (tp->snd_cwnd < win_thresh)
-                return BETA_BASE;
-
         d2 = dm / 10;
         if (da <= d2)
                 return BETA_MIN;
+
         d3 = (8 * dm) / 10;
         if (da >= d3 || d3 <= d2)
                 return BETA_MAX;
@@ -222,31 +218,107 @@ static inline u32 beta(struct sock *sk)
                 / (d3 - d2);
 }
 
+/* Update alpha and beta values once per RTT */
+static void update_params(struct sock *sk)
+{
+        struct tcp_sock *tp = tcp_sk(sk);
+        struct illinois *ca = inet_csk_ca(sk);
+
+        if (tp->snd_cwnd < win_thresh) {
+                ca->alpha = ALPHA_BASE;
+                ca->beta = BETA_BASE;
+        } else if (ca->cnt_rtt > 0) {
+                u32 dm = max_delay(ca);
+                u32 da = avg_delay(ca);
+
+                ca->alpha = alpha(ca, da, dm);
+                ca->beta = beta(da, dm);
+        }
+
+        rtt_reset(sk);
+}
+
+/*
+ * In case of loss, reset to default values
+ */
+static void tcp_illinois_state(struct sock *sk, u8 new_state)
+{
+        struct illinois *ca = inet_csk_ca(sk);
+
+        if (new_state == TCP_CA_Loss) {
+                ca->alpha = ALPHA_BASE;
+                ca->beta = BETA_BASE;
+                ca->rtt_low = 0;
+                ca->rtt_above = 0;
+                rtt_reset(sk);
+        }
+}
+
+/*
+ * Increase window in response to successful acknowledgment.
+ */
+static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
+                                    u32 in_flight, int flag)
+{
+        struct tcp_sock *tp = tcp_sk(sk);
+        struct illinois *ca = inet_csk_ca(sk);
+
+        if (after(ack, ca->end_seq))
+                update_params(sk);
+
+        /* RFC2861 only increase cwnd if fully utilized */
+        if (!tcp_is_cwnd_limited(sk, in_flight))
+                return;
+
+        /* In slow start */
+        if (tp->snd_cwnd <= tp->snd_ssthresh)
+                tcp_slow_start(tp);
+
+        else {
+                u32 delta;
+
+                /* snd_cwnd_cnt is # of packets since last cwnd increment */
+                tp->snd_cwnd_cnt += ca->acked;
+                ca->acked = 1;
+
+                /* This is close approximation of:
+                 * tp->snd_cwnd += alpha/tp->snd_cwnd
+                */
+                delta = (tp->snd_cwnd_cnt * ca->alpha) >> ALPHA_SHIFT;
+                if (delta >= tp->snd_cwnd) {
+                        tp->snd_cwnd = min(tp->snd_cwnd + delta / tp->snd_cwnd,
+                                           (u32) tp->snd_cwnd_clamp);
+                        tp->snd_cwnd_cnt = 0;
+                }
+        }
+}
+
 static u32 tcp_illinois_ssthresh(struct sock *sk)
 {
         struct tcp_sock *tp = tcp_sk(sk);
+        struct illinois *ca = inet_csk_ca(sk);
 
         /* Multiplicative decrease */
-        return max((tp->snd_cwnd * beta(sk)) >> BETA_SHIFT, 2U);
+        return max((tp->snd_cwnd * ca->beta) >> BETA_SHIFT, 2U);
 }
 
-/* Extract info for TCP socket info provided via netlink.
- * We aren't really doing Vegas, but we can provide RTT info
- */
-static void tcp_illinois_get_info(struct sock *sk, u32 ext,
-                               struct sk_buff *skb)
+
+/* Extract info for Tcp socket info provided via netlink. */
+static void tcp_illinois_info(struct sock *sk, u32 ext,
+                              struct sk_buff *skb)
 {
-        const struct tcp_illinois *ca = inet_csk_ca(sk);
+        const struct illinois *ca = inet_csk_ca(sk);
 
         if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
                 struct tcpvegas_info info = {
                         .tcpv_enabled = 1,
-                        .tcpv_rttcnt = ca->rtt_cnt,
-                        .tcpv_minrtt = ca->min_rtt,
+                        .tcpv_rttcnt = ca->cnt_rtt,
+                        .tcpv_minrtt = ca->base_rtt,
                 };
-                u64 avg_rtt = ca->sum_rtt;
-                do_div(avg_rtt, ca->rtt_cnt);
-                info.tcpv_rtt = avg_rtt;
+                u64 t = ca->sum_rtt;
+
+                do_div(t, ca->cnt_rtt);
+                info.tcpv_rtt = t;
 
                 nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
         }
@@ -257,8 +329,10 @@ static struct tcp_congestion_ops tcp_illinois = {
         .ssthresh       = tcp_illinois_ssthresh,
         .min_cwnd       = tcp_reno_min_cwnd,
         .cong_avoid     = tcp_illinois_cong_avoid,
-        .rtt_sample     = tcp_illinois_rtt_calc,
-        .get_info       = tcp_illinois_get_info,
+        .set_state      = tcp_illinois_state,
+        .rtt_sample     = tcp_illinois_rtt_sample,
+        .get_info       = tcp_illinois_info,
+        .pkts_acked     = tcp_illinois_acked,
 
         .owner          = THIS_MODULE,
         .name           = "illinois",
@@ -266,7 +340,7 @@ static struct tcp_congestion_ops tcp_illinois = {
 
 static int __init tcp_illinois_register(void)
 {
-        BUILD_BUG_ON(sizeof(struct tcp_illinois) > ICSK_CA_PRIV_SIZE);
+        BUILD_BUG_ON(sizeof(struct illinois) > ICSK_CA_PRIV_SIZE);
         return tcp_register_congestion_control(&tcp_illinois);
 }
 
@@ -281,4 +355,4 @@ module_exit(tcp_illinois_unregister);
 MODULE_AUTHOR("Stephen Hemminger, Shao Liu");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("TCP Illinois");
-MODULE_VERSION("0.3");
+MODULE_VERSION("1.0");