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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
This commit is contained in:
Hiren Panchasara
parent
385e98080c
commit
51e712f865
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=342127
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@ -102,8 +102,6 @@ struct cc_var {
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#define CCF_ACKNOW 0x0008 /* Will this ack be sent now? */
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#define CCF_IPHDR_CE 0x0010 /* Does this packet set CE bit? */
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#define CCF_TCPHDR_CWR 0x0020 /* Does this packet set CWR bit? */
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#define CCF_MAX_CWND 0x0040 /* Have we reached maximum cwnd? */
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#define CCF_CHG_MAX_CWND 0x0080 /* Cubic max_cwnd changed, for K */
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/* ACK types passed to the ack_received() hook. */
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#define CC_ACK 0x0001 /* Regular in sequence ACK. */
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@ -88,8 +88,6 @@ struct cubic {
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unsigned long max_cwnd;
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/* cwnd at the previous congestion event. */
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unsigned long prev_max_cwnd;
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/* Cached value for t_maxseg when K was computed */
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uint32_t k_maxseg;
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/* Number of congestion events. */
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uint32_t num_cong_events;
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/* Minimum observed rtt in ticks. */
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@ -126,9 +124,6 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
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cubic_data = ccv->cc_data;
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cubic_record_rtt(ccv);
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if (ccv->flags & CCF_MAX_CWND)
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return;
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/*
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* Regular ACK and we're not in cong/fast recovery and we're cwnd
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* limited and we're either not doing ABC or are slow starting or are
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@ -156,12 +151,6 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
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cubic_data->mean_rtt_ticks, cubic_data->max_cwnd,
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CCV(ccv, t_maxseg));
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if (ccv->flags & CCF_CHG_MAX_CWND || cubic_data->k_maxseg != CCV(ccv, t_maxseg)) {
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cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg));
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cubic_data->k_maxseg = CCV(ccv, t_maxseg);
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ccv->flags &= ~(CCF_MAX_CWND|CCF_CHG_MAX_CWND);
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}
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w_cubic_next = cubic_cwnd(ticks_since_cong +
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cubic_data->mean_rtt_ticks, cubic_data->max_cwnd,
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CCV(ccv, t_maxseg), cubic_data->K);
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@ -173,18 +162,13 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
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* TCP-friendly region, follow tf
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* cwnd growth.
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*/
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CCV(ccv, snd_cwnd) = ulmin(w_tf, TCP_MAXWIN << CCV(ccv, snd_scale));
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CCV(ccv, snd_cwnd) = w_tf;
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else if (CCV(ccv, snd_cwnd) < w_cubic_next) {
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/*
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* Concave or convex region, follow CUBIC
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* cwnd growth.
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*/
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if (w_cubic_next >= TCP_MAXWIN << CCV(ccv, snd_scale)) {
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w_cubic_next = TCP_MAXWIN << CCV(ccv, snd_scale);
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ccv->flags |= CCF_MAX_CWND;
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}
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w_cubic_next = ulmin(w_cubic_next, TCP_MAXWIN << CCV(ccv, snd_scale));
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if (V_tcp_do_rfc3465)
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CCV(ccv, snd_cwnd) = w_cubic_next;
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else
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@ -202,10 +186,8 @@ cubic_ack_received(struct cc_var *ccv, uint16_t type)
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* max_cwnd.
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*/
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if (cubic_data->num_cong_events == 0 &&
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cubic_data->max_cwnd < CCV(ccv, snd_cwnd)) {
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cubic_data->max_cwnd < CCV(ccv, snd_cwnd))
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cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
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ccv->flags |= CCF_CHG_MAX_CWND;
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}
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}
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}
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}
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@ -254,7 +236,6 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type)
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cubic_data->num_cong_events++;
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cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
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cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
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ccv->flags |= CCF_CHG_MAX_CWND;
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}
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ENTER_RECOVERY(CCV(ccv, t_flags));
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}
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@ -267,8 +248,6 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type)
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cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
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cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
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cubic_data->t_last_cong = ticks;
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ccv->flags |= CCF_CHG_MAX_CWND;
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ccv->flags &= ~CCF_MAX_CWND;
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CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
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ENTER_CONGRECOVERY(CCV(ccv, t_flags));
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}
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@ -285,7 +264,6 @@ cubic_cong_signal(struct cc_var *ccv, uint32_t type)
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if (CCV(ccv, t_rxtshift) >= 2) {
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cubic_data->num_cong_events++;
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cubic_data->t_last_cong = ticks;
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ccv->flags &= ~CCF_MAX_CWND;
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}
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break;
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}
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@ -304,7 +282,6 @@ cubic_conn_init(struct cc_var *ccv)
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* get used.
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*/
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cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
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ccv->flags |= CCF_CHG_MAX_CWND;
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}
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static int
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@ -329,11 +306,9 @@ cubic_post_recovery(struct cc_var *ccv)
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pipe = 0;
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/* Fast convergence heuristic. */
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if (cubic_data->max_cwnd < cubic_data->prev_max_cwnd) {
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if (cubic_data->max_cwnd < cubic_data->prev_max_cwnd)
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cubic_data->max_cwnd = (cubic_data->max_cwnd * CUBIC_FC_FACTOR)
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>> CUBIC_SHIFT;
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ccv->flags |= CCF_CHG_MAX_CWND;
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}
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if (IN_FASTRECOVERY(CCV(ccv, t_flags))) {
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/*
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@ -356,7 +331,6 @@ cubic_post_recovery(struct cc_var *ccv)
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cubic_data->max_cwnd) >> CUBIC_SHIFT));
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}
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cubic_data->t_last_cong = ticks;
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ccv->flags &= ~CCF_MAX_CWND;
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/* Calculate the average RTT between congestion epochs. */
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if (cubic_data->epoch_ack_count > 0 &&
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@ -367,6 +341,7 @@ cubic_post_recovery(struct cc_var *ccv)
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cubic_data->epoch_ack_count = 0;
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cubic_data->sum_rtt_ticks = 0;
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cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg));
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}
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/*
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@ -41,8 +41,6 @@
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#ifndef _NETINET_CC_CUBIC_H_
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#define _NETINET_CC_CUBIC_H_
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#include <sys/limits.h>
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/* Number of bits of precision for fixed point math calcs. */
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#define CUBIC_SHIFT 8
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@ -163,6 +161,8 @@ cubic_k(unsigned long wmax_pkts)
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/*
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* Compute the new cwnd value using an implementation of eqn 1 from the I-D.
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* Thanks to Kip Macy for help debugging this function.
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*
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* XXXLAS: Characterise bounds for overflow.
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*/
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static __inline unsigned long
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cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K)
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@ -174,15 +174,6 @@ cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K)
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/* t - K, with CUBIC_SHIFT worth of precision. */
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cwnd = ((int64_t)(ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz;
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/* moved this calculation up because it cannot overflow or underflow */
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cwnd *= CUBIC_C_FACTOR * smss;
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if (cwnd > 2097151) /* 2^21 cubed is long max */
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return INT_MAX;
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if (cwnd < -2097152) /* -2^21 cubed is long min */
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return smss;
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/* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */
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cwnd *= (cwnd * cwnd);
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@ -191,17 +182,8 @@ cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K)
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* The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of
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* CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above,
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* and an extra from multiplying through by CUBIC_C_FACTOR.
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*
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* The original formula was this:
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* cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax;
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*
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* CUBIC_C_FACTOR and smss factors were moved up to an earlier
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* calculation to simplify overflow and underflow detection.
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*/
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cwnd = (cwnd >> CUBIC_SHIFT_4) + wmax;
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if (cwnd < 0)
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return 1;
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cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax;
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return ((unsigned long)cwnd);
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}
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