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cc_cubic: use newreno to emulate AIMD in TCP-friendly region

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Reviewed by: rscheff, tuexen
Differential Revision: https://reviews.freebsd.org/D46546
This commit is contained in:
Cheng Cui 2024-09-05 14:52:57 -04:00
parent b6c137de0a
commit ee45061051
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GPG key ID: F9BE886D1486EF98
2 changed files with 27 additions and 35 deletions
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44
sys/netinet/cc/cc_cubic.c
View file

@ -288,31 +288,26 @@ cubic_ack_received(struct cc_var *ccv, ccsignal_t type)
usecs_since_epoch = INT_MAX;
cubic_data->t_epoch = ticks - INT_MAX;
}
W_est = tf_cwnd(ccv);
/*
* The mean RTT is used to best reflect the equations in
* the I-D. Using min_rtt in the tf_cwnd calculation
* causes W_est to grow much faster than it should if the
* RTT is dominated by network buffering rather than
* propagation delay.
* the I-D.
*/
W_est = tf_cwnd(usecs_since_epoch, cubic_data->mean_rtt_usecs,
cubic_data->W_max, CCV(ccv, t_maxseg));
W_cubic = cubic_cwnd(usecs_since_epoch +
cubic_data->mean_rtt_usecs,
cubic_data->W_max,
CCV(ccv, t_maxseg),
cubic_data->K);
ccv->flags &= ~CCF_ABC_SENTAWND;
if (W_cubic < W_est) {
/*
* TCP-friendly region, follow tf
* cwnd growth.
*/
if (CCV(ccv, snd_cwnd) < W_est)
CCV(ccv, snd_cwnd) = ulmin(W_est, INT_MAX);
CCV(ccv, snd_cwnd) = ulmin(W_est, INT_MAX);
cubic_data->flags |= CUBICFLAG_IN_TF;
} else if (CCV(ccv, snd_cwnd) < W_cubic) {
/*
* Concave or convex region, follow CUBIC
@ -320,6 +315,7 @@ cubic_ack_received(struct cc_var *ccv, ccsignal_t type)
* Only update snd_cwnd, if it doesn't shrink.
*/
CCV(ccv, snd_cwnd) = ulmin(W_cubic, INT_MAX);
cubic_data->flags &= ~CUBICFLAG_IN_TF;
}
/*
@ -644,19 +640,23 @@ cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg)
cubic_data->undo_W_max = cubic_data->W_max;
cubic_data->W_max = cwnd;
/*
* On the first congestion event, set ssthresh to cwnd * 0.5
* and reduce W_max to cwnd * beta. This aligns the cubic concave
* region appropriately. On subsequent congestion events, set
* ssthresh to cwnd * beta.
*/
if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) {
if (cubic_data->flags & CUBICFLAG_IN_TF) {
/* If in the TCP friendly region, follow what newreno does */
ssthresh = newreno_cc_cwnd_on_multiplicative_decrease(ccv, maxseg);
} else if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) {
/*
* On the first congestion event, set ssthresh to cwnd * 0.5
* and reduce W_max to cwnd * beta. This aligns the cubic
* concave region appropriately.
*/
ssthresh = cwnd >> 1;
cubic_data->W_max = ((uint64_t)cwnd *
CUBIC_BETA) >> CUBIC_SHIFT;
cubic_data->W_max = ((uint64_t)cwnd * CUBIC_BETA) >> CUBIC_SHIFT;
} else {
ssthresh = ((uint64_t)cwnd *
CUBIC_BETA) >> CUBIC_SHIFT;
/*
* On subsequent congestion events, set ssthresh to cwnd * beta.
*/
ssthresh = ((uint64_t)cwnd * CUBIC_BETA) >> CUBIC_SHIFT;
}
CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * maxseg);
}

18
sys/netinet/cc/cc_cubic.h
View file

@ -83,6 +83,7 @@
#define CUBICFLAG_RTO_EVENT 0x00000008 /* RTO experienced */
#define CUBICFLAG_HYSTART_ENABLED 0x00000010 /* Hystart++ is enabled */
#define CUBICFLAG_HYSTART_IN_CSS 0x00000020 /* We are in Hystart++ CSS */
#define CUBICFLAG_IN_TF 0x00000040 /* We are in TCP friendly region */
/* Kernel only bits */
#ifdef _KERNEL
@ -286,22 +287,13 @@ reno_cwnd(int usecs_since_epoch, int rtt_usecs, unsigned long wmax,
}
/*
* Compute an approximation of the "TCP friendly" cwnd some number of usecs
* after a congestion event that is designed to yield the same average cwnd as
* NewReno while using CUBIC's beta of 0.7. RTT should be the average RTT
* estimate for the path measured over the previous congestion epoch and wmax is
* the value of cwnd at the last congestion event.
* Compute the "TCP friendly" cwnd by newreno in congestion avoidance state.
*/
static __inline unsigned long
tf_cwnd(int usecs_since_epoch, int rtt_usecs, unsigned long wmax,
uint32_t smss)
tf_cwnd(struct cc_var *ccv)
{
/* Equation 4 of I-D. */
return (((wmax * CUBIC_BETA) +
(((THREE_X_PT3 * (unsigned long)usecs_since_epoch *
(unsigned long)smss) << CUBIC_SHIFT) / (TWO_SUB_PT3 * rtt_usecs)))
>> CUBIC_SHIFT);
/* newreno is "TCP friendly" */
return newreno_cc_cwnd_in_cong_avoid(ccv);
}
#endif /* _NETINET_CC_CUBIC_H_ */