Author: hiren
Date: Sat Dec 15 17:01:16 2018
New Revision: 342127
URL: https://svnweb.freebsd.org/changeset/base/342127
Log:
Revert r331567 CC Cubic: fix underflow for cubic_cwnd()
This change is causing TCP connections using cubic to hang. Need to dig more
to
find exact cause and fix it.
Reported by: tj at mrsk dot me, Matt Garber (via twitter)
Discussed with: sbruno (previously), allanjude, cperciva
MFC after: 3 days
Modified:
head/sys/netinet/cc/cc.h
head/sys/netinet/cc/cc_cubic.c
head/sys/netinet/cc/cc_cubic.h
Modified: head/sys/netinet/cc/cc.h
==============================================================================
--- head/sys/netinet/cc/cc.h Sat Dec 15 16:53:15 2018 (r342126)
+++ head/sys/netinet/cc/cc.h Sat Dec 15 17:01:16 2018 (r342127)
@@ -102,8 +102,6 @@ struct cc_var {
#define CCF_ACKNOW 0x0008 /* Will this ack be sent now? */
#define CCF_IPHDR_CE 0x0010 /* Does this packet set CE bit?
*/
#define CCF_TCPHDR_CWR 0x0020 /* Does this packet set CWR
bit? */
-#define CCF_MAX_CWND 0x0040 /* Have we reached maximum
cwnd? */
-#define CCF_CHG_MAX_CWND 0x0080 /* Cubic max_cwnd changed, for
K */
/* ACK types passed to the ack_received() hook. */
#define CC_ACK 0x0001 /* Regular in sequence ACK. */
Modified: head/sys/netinet/cc/cc_cubic.c
==============================================================================
--- head/sys/netinet/cc/cc_cubic.c Sat Dec 15 16:53:15 2018
(r342126)
+++ head/sys/netinet/cc/cc_cubic.c Sat Dec 15 17:01:16 2018
(r342127)
@@ -88,8 +88,6 @@ struct cubic {
unsigned long max_cwnd;
/* cwnd at the previous congestion event. */
unsigned long prev_max_cwnd;
- /* Cached value for t_maxseg when K was computed */
- uint32_t k_maxseg;
/* Number of congestion events. */
uint32_t num_cong_events;
/* Minimum observed rtt in ticks. */
@@ -126,9 +124,6 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
cubic_data = ccv->cc_data;
cubic_record_rtt(ccv);
- if (ccv->flags & CCF_MAX_CWND)
- return;
-
/*
* Regular ACK and we're not in cong/fast recovery and we're cwnd
* limited and we're either not doing ABC or are slow starting or are
@@ -156,12 +151,6 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
cubic_data->mean_rtt_ticks, cubic_data->max_cwnd,
CCV(ccv, t_maxseg));
- if (ccv->flags & CCF_CHG_MAX_CWND ||
cubic_data->k_maxseg != CCV(ccv, t_maxseg)) {
- cubic_data->K = cubic_k(cubic_data->max_cwnd /
CCV(ccv, t_maxseg));
- cubic_data->k_maxseg = CCV(ccv, t_maxseg);
- ccv->flags &= ~(CCF_MAX_CWND|CCF_CHG_MAX_CWND);
- }
-
w_cubic_next = cubic_cwnd(ticks_since_cong +
cubic_data->mean_rtt_ticks, cubic_data->max_cwnd,
CCV(ccv, t_maxseg), cubic_data->K);
@@ -173,18 +162,13 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
* TCP-friendly region, follow tf
* cwnd growth.
*/
- CCV(ccv, snd_cwnd) = ulmin(w_tf, TCP_MAXWIN <<
CCV(ccv, snd_scale));
+ CCV(ccv, snd_cwnd) = w_tf;
else if (CCV(ccv, snd_cwnd) < w_cubic_next) {
/*
* Concave or convex region, follow CUBIC
* cwnd growth.
*/
- if (w_cubic_next >= TCP_MAXWIN << CCV(ccv,
snd_scale)) {
- w_cubic_next = TCP_MAXWIN << CCV(ccv,
snd_scale);
- ccv->flags |= CCF_MAX_CWND;
- }
- w_cubic_next = ulmin(w_cubic_next, TCP_MAXWIN
<< CCV(ccv, snd_scale));
if (V_tcp_do_rfc3465)
CCV(ccv, snd_cwnd) = w_cubic_next;
else
@@ -202,10 +186,8 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
* max_cwnd.
*/
if (cubic_data->num_cong_events == 0 &&
- cubic_data->max_cwnd < CCV(ccv, snd_cwnd)) {
+ cubic_data->max_cwnd < CCV(ccv, snd_cwnd))
cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
- ccv->flags |= CCF_CHG_MAX_CWND;
- }
}
}
}
@@ -254,7 +236,6 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type)
cubic_data->num_cong_events++;
cubic_data->prev_max_cwnd =
cubic_data->max_cwnd;
cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
- ccv->flags |= CCF_CHG_MAX_CWND;
}
ENTER_RECOVERY(CCV(ccv, t_flags));
}
@@ -267,8 +248,6 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type)
cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
cubic_data->t_last_cong = ticks;
- ccv->flags |= CCF_CHG_MAX_CWND;
- ccv->flags &= ~CCF_MAX_CWND;
CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
ENTER_CONGRECOVERY(CCV(ccv, t_flags));
}
@@ -285,7 +264,6 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type)
if (CCV(ccv, t_rxtshift) >= 2) {
cubic_data->num_cong_events++;
cubic_data->t_last_cong = ticks;
- ccv->flags &= ~CCF_MAX_CWND;
}
break;
}
@@ -304,7 +282,6 @@ cubic_conn_init(struct cc_var *ccv)
* get used.
*/
cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
- ccv->flags |= CCF_CHG_MAX_CWND;
}
static int
@@ -329,11 +306,9 @@ cubic_post_recovery(struct cc_var *ccv)
pipe = 0;
/* Fast convergence heuristic. */
- if (cubic_data->max_cwnd < cubic_data->prev_max_cwnd) {
+ if (cubic_data->max_cwnd < cubic_data->prev_max_cwnd)
cubic_data->max_cwnd = (cubic_data->max_cwnd * CUBIC_FC_FACTOR)
>> CUBIC_SHIFT;
- ccv->flags |= CCF_CHG_MAX_CWND;
- }
if (IN_FASTRECOVERY(CCV(ccv, t_flags))) {
/*
@@ -356,7 +331,6 @@ cubic_post_recovery(struct cc_var *ccv)
cubic_data->max_cwnd) >> CUBIC_SHIFT));
}
cubic_data->t_last_cong = ticks;
- ccv->flags &= ~CCF_MAX_CWND;
/* Calculate the average RTT between congestion epochs. */
if (cubic_data->epoch_ack_count > 0 &&
@@ -367,6 +341,7 @@ cubic_post_recovery(struct cc_var *ccv)
cubic_data->epoch_ack_count = 0;
cubic_data->sum_rtt_ticks = 0;
+ cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg));
}
/*
Modified: head/sys/netinet/cc/cc_cubic.h
==============================================================================
--- head/sys/netinet/cc/cc_cubic.h Sat Dec 15 16:53:15 2018
(r342126)
+++ head/sys/netinet/cc/cc_cubic.h Sat Dec 15 17:01:16 2018
(r342127)
@@ -41,8 +41,6 @@
#ifndef _NETINET_CC_CUBIC_H_
#define _NETINET_CC_CUBIC_H_
-#include <sys/limits.h>
-
/* Number of bits of precision for fixed point math calcs. */
#define CUBIC_SHIFT 8
@@ -163,6 +161,8 @@ cubic_k(unsigned long wmax_pkts)
/*
* Compute the new cwnd value using an implementation of eqn 1 from the I-D.
* Thanks to Kip Macy for help debugging this function.
+ *
+ * XXXLAS: Characterise bounds for overflow.
*/
static __inline unsigned long
cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K)
@@ -174,15 +174,6 @@ cubic_cwnd(int ticks_since_cong, unsigned long wmax, u
/* t - K, with CUBIC_SHIFT worth of precision. */
cwnd = ((int64_t)(ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz;
- /* moved this calculation up because it cannot overflow or underflow */
- cwnd *= CUBIC_C_FACTOR * smss;
-
- if (cwnd > 2097151) /* 2^21 cubed is long max */
- return INT_MAX;
-
- if (cwnd < -2097152) /* -2^21 cubed is long min */
- return smss;
-
/* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */
cwnd *= (cwnd * cwnd);
@@ -191,17 +182,8 @@ cubic_cwnd(int ticks_since_cong, unsigned long wmax, u
* The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of
* CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above,
* and an extra from multiplying through by CUBIC_C_FACTOR.
- *
- * The original formula was this:
- * cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax;
- *
- * CUBIC_C_FACTOR and smss factors were moved up to an earlier
- * calculation to simplify overflow and underflow detection.
*/
- cwnd = (cwnd >> CUBIC_SHIFT_4) + wmax;
-
- if (cwnd < 0)
- return 1;
+ cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax;
return ((unsigned long)cwnd);
}
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