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D8021.1775910541.diff
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Index: sys/netinet/cc/cc_cubic.h
===================================================================
--- sys/netinet/cc/cc_cubic.h
+++ sys/netinet/cc/cc_cubic.h
@@ -42,6 +42,8 @@
/* Number of bits of precision for fixed point math calcs. */
#define CUBIC_SHIFT 8
+#define CUBIC_SCALE (1<<CUBIC_SHIFT)
+
#define CUBIC_SHIFT_4 32
/* 0.5 << CUBIC_SHIFT. */
@@ -223,7 +225,7 @@
/* Equation 4 of I-D. */
return (((wmax * CUBIC_BETA) + (((THREE_X_PT2 * ticks_since_cong *
- smss) << CUBIC_SHIFT) / TWO_SUB_PT2 / rtt_ticks)) >> CUBIC_SHIFT);
+ smss) << CUBIC_SHIFT) / (TWO_SUB_PT2 * rtt_ticks))) >> CUBIC_SHIFT);
}
#endif /* _NETINET_CC_CUBIC_H_ */
Index: sys/netinet/cc/cc_cubic.c
===================================================================
--- sys/netinet/cc/cc_cubic.c
+++ sys/netinet/cc/cc_cubic.c
@@ -96,11 +96,23 @@
int epoch_ack_count;
/* Time of last congestion event in ticks. */
int t_last_cong;
+ /* Time of last congestion event in ticks for previous event. */
+ int t_last_cong_prev;
};
static MALLOC_DEFINE(M_CUBIC, "cubic data",
"Per connection data required for the CUBIC congestion control algorithm");
+
+/* Declare sysctl tree and populate it. */
+SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, cubic, CTLFLAG_RW, NULL,
+ "cubic congestion control related settings");
+
+static int fast_convergence = 1;
+SYSCTL_INT(_net_inet_tcp_cc_cubic, OID_AUTO, fast_convergence, CTLFLAG_RWTUN,
+ &fast_convergence, 0, "Enable fast convergence as specified in Section 3.6.");
+
+
struct cc_algo cubic_cc_algo = {
.name = "cubic",
.ack_received = cubic_ack_received,
@@ -243,7 +255,6 @@
if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
cubic_ssthresh_update(ccv);
cubic_data->num_cong_events++;
- cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
}
ENTER_RECOVERY(CCV(ccv, t_flags));
@@ -254,25 +265,31 @@
if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
cubic_ssthresh_update(ccv);
cubic_data->num_cong_events++;
- cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
cubic_data->t_last_cong = ticks;
+ /*
+ * cubic_ssthresh_update(ccv) sets ssthresh to cwnd scaled by beta
+ * so this assignment is equivalent
+ */
CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
ENTER_CONGRECOVERY(CCV(ccv, t_flags));
}
break;
case CC_RTO:
- /*
- * Grab the current time and record it so we know when the
- * most recent congestion event was. Only record it when the
- * timeout has fired more than once, as there is a reasonable
- * chance the first one is a false alarm and may not indicate
- * congestion.
- */
- if (CCV(ccv, t_rxtshift) >= 2)
- cubic_data->num_cong_events++;
- cubic_data->t_last_cong = ticks;
+ if (CCV(ccv, t_rxtshift) == 1)
+ cubic_data->t_last_cong_prev = cubic_data->t_last_cong;
+ cubic_ssthresh_update(ccv);
+ cubic_data->num_cong_events++;
+ cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
+ cubic_data->t_last_cong = ticks;
+ CCV(ccv, snd_cwnd) = CCV(ccv, t_maxseg);
+ break;
+
+ case CC_RTO_ERR:
+ cubic_data->num_cong_events--;
+ cubic_data->t_last_cong = cubic_data->t_last_cong_prev;
+ cubic_data->max_cwnd = max(cubic_data->max_cwnd, cubic_data->prev_max_cwnd);
break;
}
}
@@ -401,19 +418,52 @@
static void
cubic_ssthresh_update(struct cc_var *ccv)
{
- struct cubic *cubic_data;
+ struct cubic *cd;
+ u_long snd_ssthresh, snd_cwnd;
+
+ cd = ccv->cc_data;
+
+/* 3.5. Multiplicative decrease
+ *
+ * When a packet loss occurs, CUBIC reduces its window size by a factor
+ * of beta. Parameter beta_cubic SHOULD be set to 0.7.
+ *
+ * W_max = cwnd; // save window size before reduction
+ * cwnd = cwnd * beta_cubic; // window reduction
+ */
+ snd_ssthresh = (CCV(ccv, snd_cwnd) * CUBIC_BETA) >> CUBIC_SHIFT;
+ CCV(ccv, snd_ssthresh) = max(snd_ssthresh, 2*CCV(ccv, t_maxseg));
+
+/* 3.6. Fast convergence
+ *
+ * To improve the convergence speed of CUBIC, we add a heuristic in the
+ * protocol. When a new flow joins the network, existing flows in the
+ * network need to give up their bandwidth shares to allow the flow some
+ * room for growth if the existing flows have been using all the
+ * bandwidth of the network. To increase this release of bandwidth by
+ * existing flows, the following mechanism called fast convergence
+ * SHOULD be implemented.
+ *
+ * With fast convergence, when a loss event occurs, before a window
+ * reduction of congestion window, a flow remembers the last value of
+ * W_max before it updates W_max for the current loss event. Let us
+ * call the last value of W_max to be W_last_max.
+ *
+ * if (W_max < W_last_max){ // check downward trend
+ * W_last_max = W_max; // remember the last W_max
+ * W_max = W_max*(1+beta_cubic)/2; // further reduce W_max
+ * } else { // check upward trend
+ * W_last_max = W_max // remember the last W_max
+ * }
+ */
- cubic_data = ccv->cc_data;
+ snd_cwnd = CCV(ccv, snd_cwnd);
- /*
- * On the first congestion event, set ssthresh to cwnd * 0.5, on
- * subsequent congestion events, set it to cwnd * beta.
- */
- if (cubic_data->num_cong_events == 0)
- CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd) >> 1;
+ if (snd_cwnd < cd->prev_max_cwnd && fast_convergence)
+ cd->prev_max_cwnd = (snd_cwnd * (CUBIC_SCALE + CUBIC_BETA))
+ / (2 * CUBIC_SCALE);
else
- CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_cwnd) * CUBIC_BETA)
- >> CUBIC_SHIFT;
+ cd->prev_max_cwnd = snd_cwnd;
}
Index: sys/netinet/cc/cc_dctcp.c
===================================================================
--- sys/netinet/cc/cc_dctcp.c
+++ sys/netinet/cc/cc_dctcp.c
@@ -232,7 +232,7 @@
dctcp_cong_signal(struct cc_var *ccv, uint32_t type)
{
struct dctcp *dctcp_data;
- u_int win, mss;
+ u_long win, mss;
dctcp_data = ccv->cc_data;
win = CCV(ccv, snd_cwnd);
@@ -287,6 +287,8 @@
dctcp_data->save_sndnxt += CCV(ccv, t_maxseg);
dctcp_data->num_cong_events++;
}
+ CCV(ccv, snd_ssthresh) = max(2*mss, win/2);
+ CCV(ccv, snd_cwnd) = mss;
break;
}
}
Index: sys/netinet/cc/cc_htcp.c
===================================================================
--- sys/netinet/cc/cc_htcp.c
+++ sys/netinet/cc/cc_htcp.c
@@ -271,7 +271,10 @@
htcp_cong_signal(struct cc_var *ccv, uint32_t type)
{
struct htcp *htcp_data;
+ u_long win, mss;
+ win = CCV(ccv, snd_cwnd);
+ mss = CCV(ccv, t_maxseg);
htcp_data = ccv->cc_data;
switch (type) {
@@ -320,6 +323,8 @@
*/
if (CCV(ccv, t_rxtshift) >= 2)
htcp_data->t_last_cong = ticks;
+ CCV(ccv, snd_ssthresh) = max(2*mss, win/2);
+ CCV(ccv, snd_cwnd) = mss;
break;
}
}
Index: sys/netinet/cc/cc_newreno.c
===================================================================
--- sys/netinet/cc/cc_newreno.c
+++ sys/netinet/cc/cc_newreno.c
@@ -184,14 +184,16 @@
static void
newreno_cong_signal(struct cc_var *ccv, uint32_t type)
{
- u_int win;
+ u_long win, mss;
+
+ win = CCV(ccv, snd_cwnd);
+ mss = CCV(ccv, t_maxseg);
/* Catch algos which mistakenly leak private signal types. */
KASSERT((type & CC_SIGPRIVMASK) == 0,
("%s: congestion signal type 0x%08x is private\n", __func__, type));
- win = max(CCV(ccv, snd_cwnd) / 2 / CCV(ccv, t_maxseg), 2) *
- CCV(ccv, t_maxseg);
+ win = max(2*mss, win/2);
switch (type) {
case CC_NDUPACK:
@@ -208,6 +210,10 @@
ENTER_CONGRECOVERY(CCV(ccv, t_flags));
}
break;
+ case CC_RTO:
+ CCV(ccv, snd_ssthresh) = win;
+ CCV(ccv, snd_cwnd) = mss;
+ break;
}
}
Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -321,8 +321,10 @@
if (type == CC_ACK) {
if (tp->snd_cwnd > tp->snd_ssthresh) {
+ /* Do we really need to filter out stretch ACKs? */
tp->t_bytes_acked += min(tp->ccv->bytes_this_ack,
V_tcp_abc_l_var * tp->t_maxseg);
+
if (tp->t_bytes_acked >= tp->snd_cwnd) {
tp->t_bytes_acked -= tp->snd_cwnd;
tp->ccv->flags |= CCF_ABC_SENTAWND;
@@ -436,9 +438,11 @@
tp->t_dupacks = 0;
tp->t_bytes_acked = 0;
EXIT_RECOVERY(tp->t_flags);
- tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
- tp->t_maxseg) * tp->t_maxseg;
- tp->snd_cwnd = tp->t_maxseg;
+ if (CC_ALGO(tp)->cong_signal == NULL) {
+ tp->snd_ssthresh = max(2, min(tp->snd_wnd, tp->snd_cwnd) / 2 /
+ tp->t_maxseg) * tp->t_maxseg;
+ tp->snd_cwnd = tp->t_maxseg;
+ }
break;
case CC_RTO_ERR:
TCPSTAT_INC(tcps_sndrexmitbad);

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