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tcp: Use segment size excluding tcp options for all cwnd calculations
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Avoid sending small segments by making sure that cwnd is usually
calculated in full (data) segment sizes. Especially during loss
recovery and retransmission scenarios.

Reviewed By: tuexen, #transport
Sponsored by: NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D47474
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@rscheff
rscheff committed Nov 14, 2024
1 parent 8f5a2e2 commit 22dcc81
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Showing 9 changed files with 61 additions and 54 deletions.
13 changes: 7 additions & 6 deletions sys/netinet/cc/cc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -392,6 +392,7 @@ void
newreno_cc_post_recovery(struct cc_var *ccv)
{
int pipe;
uint32_t mss = tcp_fixed_maxseg(ccv->tp);

if (IN_FASTRECOVERY(CCV(ccv, t_flags))) {
/*
Expand All @@ -412,8 +413,7 @@ newreno_cc_post_recovery(struct cc_var *ccv)
* Ensure that cwnd does not collapse to 1 MSS under
* adverse conditions. Implements RFC6582
*/
CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) +
CCV(ccv, t_maxseg);
CCV(ccv, snd_cwnd) = max(pipe, mss) + mss;
else
CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
}
Expand Down Expand Up @@ -521,7 +521,7 @@ u_int
newreno_cc_cwnd_in_cong_avoid(struct cc_var *ccv)
{
u_int cw = CCV(ccv, snd_cwnd);
u_int incr = CCV(ccv, t_maxseg);
u_int incr = tcp_fixed_maxseg(ccv->tp);

KASSERT(cw > CCV(ccv, snd_ssthresh),
("congestion control state not in congestion avoidance\n"));
Expand Down Expand Up @@ -561,7 +561,8 @@ u_int
newreno_cc_cwnd_in_slow_start(struct cc_var *ccv)
{
u_int cw = CCV(ccv, snd_cwnd);
u_int incr = CCV(ccv, t_maxseg);
u_int mss = tcp_fixed_maxseg(ccv->tp);
u_int incr = mss;

KASSERT(cw <= CCV(ccv, snd_ssthresh),
("congestion control state not in slow start\n"));
Expand Down Expand Up @@ -599,9 +600,9 @@ newreno_cc_cwnd_in_slow_start(struct cc_var *ccv)
abc_val = V_tcp_abc_l_var;
if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max))
incr = min(ccv->bytes_this_ack,
ccv->nsegs * abc_val * CCV(ccv, t_maxseg));
ccv->nsegs * abc_val * mss);
else
incr = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg));
incr = min(ccv->bytes_this_ack, mss);
}
/* ABC is on by default, so incr equals 0 frequently. */
if (incr > 0)
Expand Down
9 changes: 5 additions & 4 deletions sys/netinet/cc/cc_cdg.c
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Original file line number Diff line number Diff line change
Expand Up @@ -416,27 +416,28 @@ cdg_window_increase(struct cc_var *ccv, int new_measurement)
{
struct cdg *cdg_data;
int incr, s_w_incr;
uint32_t mss = tcp_fixed_maxseg(ccv->tp);

cdg_data = ccv->cc_data;
incr = s_w_incr = 0;

if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh)) {
/* Slow start. */
incr = CCV(ccv, t_maxseg);
incr = mss;
s_w_incr = incr;
cdg_data->window_incr = cdg_data->rtt_count = 0;
} else {
/* Congestion avoidance. */
if (new_measurement) {
s_w_incr = CCV(ccv, t_maxseg);
s_w_incr = mss;
if (V_cdg_alpha_inc == 0) {
incr = CCV(ccv, t_maxseg);
incr = mss;
} else {
if (++cdg_data->rtt_count >= V_cdg_alpha_inc) {
cdg_data->window_incr++;
cdg_data->rtt_count = 0;
}
incr = CCV(ccv, t_maxseg) *
incr = mss *
cdg_data->window_incr;
}
}
Expand Down
20 changes: 11 additions & 9 deletions sys/netinet/cc/cc_chd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -147,10 +147,11 @@ static __inline void
chd_window_decrease(struct cc_var *ccv)
{
unsigned long win;
uint32_t mss = tcp_fixed_maxseg(ccv->tp);

win = min(CCV(ccv, snd_wnd), CCV(ccv, snd_cwnd)) / CCV(ccv, t_maxseg);
win = min(CCV(ccv, snd_wnd), CCV(ccv, snd_cwnd)) / mss;
win -= max((win / 2), 1);
CCV(ccv, snd_ssthresh) = max(win, 2) * CCV(ccv, t_maxseg);
CCV(ccv, snd_ssthresh) = max(win, 2) * mss;
}

/*
Expand Down Expand Up @@ -190,6 +191,7 @@ chd_window_increase(struct cc_var *ccv, int new_measurement)
{
struct chd *chd_data;
int incr;
uint32_t mss = tcp_fixed_maxseg(ccv->tp);

chd_data = ccv->cc_data;
incr = 0;
Expand All @@ -201,23 +203,22 @@ chd_window_increase(struct cc_var *ccv, int new_measurement)
if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max)) {
/* Not due to RTO. */
incr = min(ccv->bytes_this_ack,
V_tcp_abc_l_var * CCV(ccv, t_maxseg));
V_tcp_abc_l_var * mss);
} else {
/* Due to RTO. */
incr = min(ccv->bytes_this_ack,
CCV(ccv, t_maxseg));
incr = min(ccv->bytes_this_ack, mss);
}
} else
incr = CCV(ccv, t_maxseg);
incr = mss;

} else { /* Congestion avoidance. */
if (V_tcp_do_rfc3465) {
if (ccv->flags & CCF_ABC_SENTAWND) {
ccv->flags &= ~CCF_ABC_SENTAWND;
incr = CCV(ccv, t_maxseg);
incr = mss;
}
} else if (new_measurement)
incr = CCV(ccv, t_maxseg);
incr = mss;
}

if (chd_data->shadow_w > 0) {
Expand Down Expand Up @@ -380,8 +381,9 @@ chd_cong_signal(struct cc_var *ccv, ccsignal_t signal_type)
}

if (chd_data->shadow_w > 0) {
uint32_t mss = tcp_fixed_maxseg(ccv->tp);
chd_data->shadow_w = max(chd_data->shadow_w /
CCV(ccv, t_maxseg) / 2, 2) * CCV(ccv, t_maxseg);
mss / 2, 2) * mss;
}
ENTER_FASTRECOVERY(CCV(ccv, t_flags));
break;
Expand Down
24 changes: 12 additions & 12 deletions sys/netinet/cc/cc_cubic.c
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Original file line number Diff line number Diff line change
Expand Up @@ -168,7 +168,8 @@ cubic_does_slow_start(struct cc_var *ccv, struct cubic *cubicd)
* doesn't rely on tcpcb vars.
*/
u_int cw = CCV(ccv, snd_cwnd);
u_int incr = CCV(ccv, t_maxseg);
uint32_t mss = tcp_fixed_maxseg(ccv->tp);
u_int incr = mss;
uint16_t abc_val;

cubicd->flags |= CUBICFLAG_IN_SLOWSTART;
Expand Down Expand Up @@ -216,10 +217,9 @@ cubic_does_slow_start(struct cc_var *ccv, struct cubic *cubicd)
}
if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max))
incr = min(ccv->bytes_this_ack,
ccv->nsegs * abc_val *
CCV(ccv, t_maxseg));
ccv->nsegs * abc_val * mss);
else
incr = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg));
incr = min(ccv->bytes_this_ack, mss);

/* Only if Hystart is enabled will the flag get set */
if (cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) {
Expand All @@ -238,6 +238,7 @@ cubic_ack_received(struct cc_var *ccv, ccsignal_t type)
struct cubic *cubic_data;
unsigned long W_est, W_cubic;
int usecs_since_epoch;
uint32_t mss = tcp_fixed_maxseg(ccv->tp);

cubic_data = ccv->cc_data;
cubic_record_rtt(ccv);
Expand Down Expand Up @@ -277,8 +278,7 @@ cubic_ack_received(struct cc_var *ccv, ccsignal_t type)
cubic_data->flags &= ~(CUBICFLAG_IN_SLOWSTART |
CUBICFLAG_IN_APPLIMIT);
cubic_data->t_epoch = ticks;
cubic_data->K = cubic_k(cubic_data->W_max /
CCV(ccv, t_maxseg));
cubic_data->K = cubic_k(cubic_data->W_max / mss);
}
usecs_since_epoch = (ticks - cubic_data->t_epoch) * tick;
if (usecs_since_epoch < 0) {
Expand All @@ -298,7 +298,7 @@ cubic_ack_received(struct cc_var *ccv, ccsignal_t type)
W_cubic = cubic_cwnd(usecs_since_epoch +
cubic_data->mean_rtt_usecs,
cubic_data->W_max,
CCV(ccv, t_maxseg),
tcp_fixed_maxseg(ccv->tp),
cubic_data->K);

if (W_cubic < W_est) {
Expand Down Expand Up @@ -329,7 +329,7 @@ cubic_ack_received(struct cc_var *ccv, ccsignal_t type)
cubic_data->W_max < CCV(ccv, snd_cwnd)) {
cubic_data->W_max = CCV(ccv, snd_cwnd);
cubic_data->K = cubic_k(cubic_data->W_max /
CCV(ccv, t_maxseg));
tcp_fixed_maxseg(ccv->tp));
}
}
} else if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
Expand All @@ -351,7 +351,7 @@ cubic_after_idle(struct cc_var *ccv)
cubic_data = ccv->cc_data;

cubic_data->W_max = ulmax(cubic_data->W_max, CCV(ccv, snd_cwnd));
cubic_data->K = cubic_k(cubic_data->W_max / CCV(ccv, t_maxseg));
cubic_data->K = cubic_k(cubic_data->W_max / tcp_fixed_maxseg(ccv->tp));
if ((cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) == 0) {
/*
* Re-enable hystart if we have been idle.
Expand Down Expand Up @@ -532,6 +532,7 @@ cubic_post_recovery(struct cc_var *ccv)
{
struct cubic *cubic_data;
int pipe;
uint32_t mss = tcp_fixed_maxseg(ccv->tp);

cubic_data = ccv->cc_data;
pipe = 0;
Expand All @@ -554,13 +555,12 @@ cubic_post_recovery(struct cc_var *ccv)
* Ensure that cwnd does not collapse to 1 MSS under
* adverse conditions. Implements RFC6582
*/
CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) +
CCV(ccv, t_maxseg);
CCV(ccv, snd_cwnd) = max(pipe, mss) + mss;
else
/* Update cwnd based on beta and adjusted W_max. */
CCV(ccv, snd_cwnd) = max(((uint64_t)cubic_data->W_max *
CUBIC_BETA) >> CUBIC_SHIFT,
2 * CCV(ccv, t_maxseg));
2 * mss);
}

/* Calculate the average RTT between congestion epochs. */
Expand Down
13 changes: 7 additions & 6 deletions sys/netinet/cc/cc_dctcp.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -108,6 +108,7 @@ dctcp_ack_received(struct cc_var *ccv, ccsignal_t type)
{
struct dctcp *dctcp_data;
int bytes_acked = 0;
uint32_t mss = tcp_fixed_maxseg(ccv->tp);

dctcp_data = ccv->cc_data;

Expand All @@ -125,7 +126,7 @@ dctcp_ack_received(struct cc_var *ccv, ccsignal_t type)
newreno_cc_ack_received(ccv, type);

if (type == CC_DUPACK)
bytes_acked = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg));
bytes_acked = min(ccv->bytes_this_ack, mss);

if (type == CC_ACK)
bytes_acked = ccv->bytes_this_ack;
Expand All @@ -138,16 +139,16 @@ dctcp_ack_received(struct cc_var *ccv, ccsignal_t type)
//XXRMS: For fluid-model DCTCP, update
//cwnd here during for RTT fairness
if (!dctcp_data->ece_prev
&& bytes_acked > CCV(ccv, t_maxseg)) {
&& bytes_acked > mss) {
dctcp_data->bytes_ecn +=
(bytes_acked - CCV(ccv, t_maxseg));
(bytes_acked - mss);
} else
dctcp_data->bytes_ecn += bytes_acked;
dctcp_data->ece_prev = 1;
} else {
if (dctcp_data->ece_prev
&& bytes_acked > CCV(ccv, t_maxseg))
dctcp_data->bytes_ecn += CCV(ccv, t_maxseg);
&& bytes_acked > mss)
dctcp_data->bytes_ecn += mss;
dctcp_data->ece_prev = 0;
}
dctcp_data->ece_curr = 0;
Expand Down Expand Up @@ -305,7 +306,7 @@ dctcp_cong_signal(struct cc_var *ccv, ccsignal_t type)
}
CCV(ccv, snd_cwnd) = mss;
dctcp_update_alpha(ccv);
dctcp_data->save_sndnxt += CCV(ccv, t_maxseg);
dctcp_data->save_sndnxt += mss;
dctcp_data->num_cong_events++;
break;
default:
Expand Down
15 changes: 8 additions & 7 deletions sys/netinet/cc/cc_htcp.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -193,6 +193,7 @@ static void
htcp_ack_received(struct cc_var *ccv, ccsignal_t type)
{
struct htcp *htcp_data;
uint32_t mss = tcp_fixed_maxseg(ccv->tp);

htcp_data = ccv->cc_data;
htcp_record_rtt(ccv);
Expand Down Expand Up @@ -220,7 +221,7 @@ htcp_ack_received(struct cc_var *ccv, ccsignal_t type)
if (V_tcp_do_rfc3465) {
/* Increment cwnd by alpha segments. */
CCV(ccv, snd_cwnd) += htcp_data->alpha *
CCV(ccv, t_maxseg);
mss;
ccv->flags &= ~CCF_ABC_SENTAWND;
} else
/*
Expand All @@ -230,8 +231,8 @@ htcp_ack_received(struct cc_var *ccv, ccsignal_t type)
*/
CCV(ccv, snd_cwnd) += (((htcp_data->alpha <<
HTCP_SHIFT) / (max(1,
CCV(ccv, snd_cwnd) / CCV(ccv, t_maxseg)))) *
CCV(ccv, t_maxseg)) >> HTCP_SHIFT;
CCV(ccv, snd_cwnd) / mss))) *
mss) >> HTCP_SHIFT;
}
}
}
Expand Down Expand Up @@ -370,6 +371,7 @@ htcp_post_recovery(struct cc_var *ccv)
{
int pipe;
struct htcp *htcp_data;
uint32_t mss = tcp_fixed_maxseg(ccv->tp);

pipe = 0;
htcp_data = ccv->cc_data;
Expand All @@ -392,12 +394,11 @@ htcp_post_recovery(struct cc_var *ccv)
* Ensure that cwnd down not collape to 1 MSS under
* adverse conditions. Implements RFC6582
*/
CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) +
CCV(ccv, t_maxseg);
CCV(ccv, snd_cwnd) = max(pipe, mss) + mss;
else
CCV(ccv, snd_cwnd) = max(1, ((htcp_data->beta *
htcp_data->prev_cwnd / CCV(ccv, t_maxseg))
>> HTCP_SHIFT)) * CCV(ccv, t_maxseg);
htcp_data->prev_cwnd / mss)
>> HTCP_SHIFT)) * mss;
}
}

Expand Down
8 changes: 4 additions & 4 deletions sys/netinet/cc/cc_newreno.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -215,12 +215,13 @@ static void
newreno_ack_received(struct cc_var *ccv, ccsignal_t type)
{
struct newreno *nreno;
uint32_t mss = tcp_fixed_maxseg(ccv->tp);

nreno = ccv->cc_data;
if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
(ccv->flags & CCF_CWND_LIMITED)) {
u_int cw = CCV(ccv, snd_cwnd);
u_int incr = CCV(ccv, t_maxseg);
u_int incr = mss;

/*
* Regular in-order ACK, open the congestion window.
Expand Down Expand Up @@ -324,10 +325,9 @@ newreno_ack_received(struct cc_var *ccv, ccsignal_t type)
}
if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max))
incr = min(ccv->bytes_this_ack,
ccv->nsegs * abc_val *
CCV(ccv, t_maxseg));
ccv->nsegs * abc_val * mss);
else
incr = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg));
incr = min(ccv->bytes_this_ack, mss);

/* Only if Hystart is enabled will the flag get set */
if (nreno->newreno_flags & CC_NEWRENO_HYSTART_IN_CSS) {
Expand Down
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