[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>
This commit is contained in:
Stephen Hemminger
David S. Miller
parent
42431592e7
commit
65d1b4a7e7
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@ -23,74 +23,106 @@
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#define ALPHA_MIN ((3*ALPHA_SCALE)/10) /* ~0.3 */
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#define ALPHA_MAX (10*ALPHA_SCALE) /* 10.0 */
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#define ALPHA_BASE ALPHA_SCALE /* 1.0 */
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#define U32_MAX ((u32)~0U)
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#define RTT_MAX (U32_MAX / ALPHA_MAX) /* 3.3 secs */
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#define BETA_SHIFT 6
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#define BETA_SCALE (1u<<BETA_SHIFT)
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#define BETA_MIN (BETA_SCALE/8) /* 0.8 */
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#define BETA_MAX (BETA_SCALE/2)
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#define BETA_BASE BETA_MAX /* 0.5 */
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#define THETA 5
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#define BETA_MIN (BETA_SCALE/8) /* 0.125 */
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#define BETA_MAX (BETA_SCALE/2) /* 0.5 */
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#define BETA_BASE BETA_MAX
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static int win_thresh __read_mostly = 15;
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module_param(win_thresh, int, 0644);
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module_param(win_thresh, int, 0);
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MODULE_PARM_DESC(win_thresh, "Window threshold for starting adaptive sizing");
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#define MAX_RTT 0x7fffffff
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static int theta __read_mostly = 5;
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module_param(theta, int, 0);
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MODULE_PARM_DESC(theta, "# of fast RTT's before full growth");
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/* TCP Illinois Parameters */
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struct tcp_illinois {
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u32 last_alpha;
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u32 min_rtt;
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u32 max_rtt;
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u32 rtt_low;
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u32 rtt_cnt;
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u64 sum_rtt;
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struct illinois {
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u64 sum_rtt; /* sum of rtt's measured within last rtt */
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u16 cnt_rtt; /* # of rtts measured within last rtt */
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u32 base_rtt; /* min of all rtt in usec */
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u32 max_rtt; /* max of all rtt in usec */
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u32 end_seq; /* right edge of current RTT */
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u32 alpha; /* Additive increase */
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u32 beta; /* Muliplicative decrease */
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u16 acked; /* # packets acked by current ACK */
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u8 rtt_above; /* average rtt has gone above threshold */
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u8 rtt_low; /* # of rtts measurements below threshold */
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};
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static void rtt_reset(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct illinois *ca = inet_csk_ca(sk);
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ca->end_seq = tp->snd_nxt;
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ca->cnt_rtt = 0;
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ca->sum_rtt = 0;
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/* TODO: age max_rtt? */
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}
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static void tcp_illinois_init(struct sock *sk)
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{
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struct tcp_illinois *ca = inet_csk_ca(sk);
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struct illinois *ca = inet_csk_ca(sk);
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ca->last_alpha = ALPHA_BASE;
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ca->min_rtt = 0x7fffffff;
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ca->alpha = ALPHA_MAX;
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ca->beta = BETA_BASE;
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ca->base_rtt = 0x7fffffff;
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ca->max_rtt = 0;
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ca->acked = 0;
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ca->rtt_low = 0;
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ca->rtt_above = 0;
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rtt_reset(sk);
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}
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/*
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* Keep track of min, max and average RTT
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*/
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static void tcp_illinois_rtt_calc(struct sock *sk, u32 rtt)
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/* Measure RTT for each ack. */
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static void tcp_illinois_rtt_sample(struct sock *sk, u32 rtt)
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{
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struct tcp_illinois *ca = inet_csk_ca(sk);
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struct illinois *ca = inet_csk_ca(sk);
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if (rtt < ca->min_rtt)
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ca->min_rtt = rtt;
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if (rtt > ca->max_rtt)
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/* ignore bogus values, this prevents wraparound in alpha math */
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if (rtt > RTT_MAX)
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rtt = RTT_MAX;
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/* keep track of minimum RTT seen so far */
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if (ca->base_rtt > rtt)
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ca->base_rtt = rtt;
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/* and max */
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if (ca->max_rtt < rtt)
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ca->max_rtt = rtt;
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if (++ca->rtt_cnt == 1)
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ca->sum_rtt = rtt;
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else
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ca->sum_rtt += rtt;
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++ca->cnt_rtt;
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ca->sum_rtt += rtt;
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}
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/* max queuing delay */
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static inline u32 max_delay(const struct tcp_illinois *ca)
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/* Capture count of packets covered by ack, to adjust for delayed acks */
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static void tcp_illinois_acked(struct sock *sk, u32 pkts_acked)
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{
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return ca->max_rtt - ca->min_rtt;
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struct illinois *ca = inet_csk_ca(sk);
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ca->acked = pkts_acked;
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}
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/* average queueing delay */
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static u32 avg_delay(struct tcp_illinois *ca)
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/* Maximum queuing delay */
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static inline u32 max_delay(const struct illinois *ca)
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{
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u64 avg_rtt = ca->sum_rtt;
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return ca->max_rtt - ca->base_rtt;
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}
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do_div(avg_rtt, ca->rtt_cnt);
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/* Average queuing delay */
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static inline u32 avg_delay(const struct illinois *ca)
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{
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u64 t = ca->sum_rtt;
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ca->sum_rtt = 0;
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ca->rtt_cnt = 0;
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return avg_rtt - ca->min_rtt;
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do_div(t, ca->cnt_rtt);
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return t - ca->base_rtt;
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}
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/*
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@ -101,32 +133,31 @@ static u32 avg_delay(struct tcp_illinois *ca)
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* A. If average delay is at minimum (we are uncongested),
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* then use large alpha (10.0) to increase faster.
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* B. If average delay is at maximum (getting congested)
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* then use small alpha (1.0)
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* then use small alpha (0.3)
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*
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* The result is a convex window growth curve.
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*/
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static u32 alpha(const struct sock *sk)
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static u32 alpha(struct illinois *ca, u32 da, u32 dm)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct tcp_illinois *ca = inet_csk_ca(sk);
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u32 dm = max_delay(ca);
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u32 da = avg_delay(ca);
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u32 d1, a;
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u32 d1 = dm / 100; /* Low threshold */
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if (tp->snd_cwnd < win_thresh)
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return ALPHA_BASE; /* same as Reno (1.0) */
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d1 = dm / 100;
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if (da <= d1) {
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/* Don't let noise force agressive response */
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if (ca->rtt_low < THETA) {
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++ca->rtt_low;
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return ca->last_alpha;
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} else
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/* If never got out of low delay zone, then use max */
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if (!ca->rtt_above)
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return ALPHA_MAX;
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/* Wait for 5 good RTT's before allowing alpha to go alpha max.
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* This prevents one good RTT from causing sudden window increase.
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*/
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if (++ca->rtt_low < theta)
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return ca->alpha;
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ca->rtt_low = 0;
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ca->rtt_above = 0;
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return ALPHA_MAX;
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}
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ca->rtt_low = 0;
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ca->rtt_above = 1;
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/*
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* Based on:
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@ -146,37 +177,8 @@ static u32 alpha(const struct sock *sk)
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dm -= d1;
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da -= d1;
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a = (dm * ALPHA_MAX) / (dm - (da * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
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ca->last_alpha = a;
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return a;
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}
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/*
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* Increase window in response to successful acknowledgment.
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*/
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static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
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u32 in_flight, int flag)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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/* RFC2861 only increase cwnd if fully utilized */
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if (!tcp_is_cwnd_limited(sk, in_flight))
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return;
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/* In slow start */
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if (tp->snd_cwnd <= tp->snd_ssthresh)
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tcp_slow_start(tp);
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else {
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/* additive increase cwnd += alpha / cwnd */
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if ((tp->snd_cwnd_cnt * alpha(sk)) >> ALPHA_SHIFT >= tp->snd_cwnd) {
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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tp->snd_cwnd_cnt = 0;
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} else
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tp->snd_cwnd_cnt++;
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}
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return (dm * ALPHA_MAX) /
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(dm + (da * (ALPHA_MAX - ALPHA_MIN)) / ALPHA_MIN);
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}
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/*
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@ -187,20 +189,14 @@ static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
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* If delay is up to 80% of max then beta = 1/2
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* In between is a linear function
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*/
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static inline u32 beta(struct sock *sk)
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static u32 beta(u32 da, u32 dm)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct tcp_illinois *ca = inet_csk_ca(sk);
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u32 dm = max_delay(ca);
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u32 da = avg_delay(ca);
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u32 d2, d3;
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if (tp->snd_cwnd < win_thresh)
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return BETA_BASE;
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d2 = dm / 10;
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if (da <= d2)
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return BETA_MIN;
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d3 = (8 * dm) / 10;
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if (da >= d3 || d3 <= d2)
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return BETA_MAX;
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@ -222,31 +218,107 @@ static inline u32 beta(struct sock *sk)
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/ (d3 - d2);
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}
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/* Update alpha and beta values once per RTT */
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static void update_params(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct illinois *ca = inet_csk_ca(sk);
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if (tp->snd_cwnd < win_thresh) {
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ca->alpha = ALPHA_BASE;
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ca->beta = BETA_BASE;
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} else if (ca->cnt_rtt > 0) {
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u32 dm = max_delay(ca);
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u32 da = avg_delay(ca);
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ca->alpha = alpha(ca, da, dm);
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ca->beta = beta(da, dm);
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}
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rtt_reset(sk);
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}
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/*
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* In case of loss, reset to default values
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*/
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static void tcp_illinois_state(struct sock *sk, u8 new_state)
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{
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struct illinois *ca = inet_csk_ca(sk);
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if (new_state == TCP_CA_Loss) {
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ca->alpha = ALPHA_BASE;
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ca->beta = BETA_BASE;
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ca->rtt_low = 0;
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ca->rtt_above = 0;
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rtt_reset(sk);
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}
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}
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/*
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* Increase window in response to successful acknowledgment.
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*/
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static void tcp_illinois_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
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u32 in_flight, int flag)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct illinois *ca = inet_csk_ca(sk);
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if (after(ack, ca->end_seq))
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update_params(sk);
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/* RFC2861 only increase cwnd if fully utilized */
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if (!tcp_is_cwnd_limited(sk, in_flight))
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return;
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/* In slow start */
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if (tp->snd_cwnd <= tp->snd_ssthresh)
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tcp_slow_start(tp);
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else {
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u32 delta;
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/* snd_cwnd_cnt is # of packets since last cwnd increment */
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tp->snd_cwnd_cnt += ca->acked;
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ca->acked = 1;
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/* This is close approximation of:
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* tp->snd_cwnd += alpha/tp->snd_cwnd
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*/
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delta = (tp->snd_cwnd_cnt * ca->alpha) >> ALPHA_SHIFT;
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if (delta >= tp->snd_cwnd) {
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tp->snd_cwnd = min(tp->snd_cwnd + delta / tp->snd_cwnd,
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(u32) tp->snd_cwnd_clamp);
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tp->snd_cwnd_cnt = 0;
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}
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}
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}
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static u32 tcp_illinois_ssthresh(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct illinois *ca = inet_csk_ca(sk);
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/* Multiplicative decrease */
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return max((tp->snd_cwnd * beta(sk)) >> BETA_SHIFT, 2U);
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return max((tp->snd_cwnd * ca->beta) >> BETA_SHIFT, 2U);
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}
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/* Extract info for TCP socket info provided via netlink.
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* We aren't really doing Vegas, but we can provide RTT info
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*/
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static void tcp_illinois_get_info(struct sock *sk, u32 ext,
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struct sk_buff *skb)
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/* Extract info for Tcp socket info provided via netlink. */
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static void tcp_illinois_info(struct sock *sk, u32 ext,
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struct sk_buff *skb)
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{
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const struct tcp_illinois *ca = inet_csk_ca(sk);
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const struct illinois *ca = inet_csk_ca(sk);
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if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
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struct tcpvegas_info info = {
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.tcpv_enabled = 1,
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.tcpv_rttcnt = ca->rtt_cnt,
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.tcpv_minrtt = ca->min_rtt,
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.tcpv_rttcnt = ca->cnt_rtt,
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.tcpv_minrtt = ca->base_rtt,
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};
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u64 avg_rtt = ca->sum_rtt;
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do_div(avg_rtt, ca->rtt_cnt);
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info.tcpv_rtt = avg_rtt;
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u64 t = ca->sum_rtt;
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do_div(t, ca->cnt_rtt);
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info.tcpv_rtt = t;
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nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info);
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}
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@ -257,8 +329,10 @@ static struct tcp_congestion_ops tcp_illinois = {
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.ssthresh = tcp_illinois_ssthresh,
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.min_cwnd = tcp_reno_min_cwnd,
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.cong_avoid = tcp_illinois_cong_avoid,
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.rtt_sample = tcp_illinois_rtt_calc,
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.get_info = tcp_illinois_get_info,
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.set_state = tcp_illinois_state,
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.rtt_sample = tcp_illinois_rtt_sample,
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.get_info = tcp_illinois_info,
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.pkts_acked = tcp_illinois_acked,
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.owner = THIS_MODULE,
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.name = "illinois",
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@ -266,7 +340,7 @@ static struct tcp_congestion_ops tcp_illinois = {
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static int __init tcp_illinois_register(void)
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{
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BUILD_BUG_ON(sizeof(struct tcp_illinois) > ICSK_CA_PRIV_SIZE);
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BUILD_BUG_ON(sizeof(struct illinois) > ICSK_CA_PRIV_SIZE);
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return tcp_register_congestion_control(&tcp_illinois);
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}
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@ -281,4 +355,4 @@ module_exit(tcp_illinois_unregister);
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MODULE_AUTHOR("Stephen Hemminger, Shao Liu");
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("TCP Illinois");
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MODULE_VERSION("0.3");
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MODULE_VERSION("1.0");
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