This patch adds TCP BIC back in as a pluggable TCP congestion mechanism.
This version is closer to the TCP BIC 1.1 released for Web100.
The changes from 2.6.11 are:
* congestion window undo fix
* delayed ack compensation
* low utilization detection
* more parameter (less hardcoded constants)
The parts that are in the Web100 version are missing are general (not BIC
specific):
* burst moderation
* network device throttling drop tail behaviour
They will be addressed later.
Signed-off-by: Stephen Hemminger <shemminger@xxxxxxxx>
diff -Nru a/net/ipv4/Kconfig b/net/ipv4/Kconfig
--- a/net/ipv4/Kconfig 2005-03-18 16:09:40 -08:00
+++ b/net/ipv4/Kconfig 2005-03-18 16:09:40 -08:00
@@ -368,6 +368,20 @@
menu "TCP congestion control"
+config TCP_CONG_BIC
+ tristate "Binary Increase Congestion (BIC) control"
+ default y
+ ---help---
+ BIC-TCP is a sender-side only change that ensures a linear RTT
+ fairness under large windows while offering both scalability and
+ bounded TCP-friendliness. The protocol combines two schemes
+ called additive increase and binary search increase. When the
+ congestion window is large, additive increase with a large
+ increment ensures linear RTT fairness as well as good
+ scalability. Under small congestion windows, binary search
+ increase provides TCP friendliness.
+ See http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/
+
endmenu
source "net/ipv4/ipvs/Kconfig"
diff -Nru a/net/ipv4/Makefile b/net/ipv4/Makefile
--- a/net/ipv4/Makefile 2005-03-18 16:09:40 -08:00
+++ b/net/ipv4/Makefile 2005-03-18 16:09:40 -08:00
@@ -24,6 +24,7 @@
obj-$(CONFIG_NETFILTER) += netfilter/
obj-$(CONFIG_IP_VS) += ipvs/
obj-$(CONFIG_IP_TCPDIAG) += tcp_diag.o
+obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
xfrm4_output.o
diff -Nru a/net/ipv4/tcp_bic.c b/net/ipv4/tcp_bic.c
--- /dev/null Wed Dec 31 16:00:00 196900
+++ b/net/ipv4/tcp_bic.c 2005-03-18 16:09:40 -08:00
@@ -0,0 +1,293 @@
+/*
+ * Binary Increase Congestion control for TCP
+ *
+ * This is from the implementation of BICTCP in
+ * Lison-Xu, Kahaled Harfoush, and Injong Rhee.
+ * "Binary Increase Congestion Control for Fast, Long Distance
+ * Networks" in InfoComm 2004
+ * Available from:
+ * http://www.csc.ncsu.edu/faculty/rhee/export/bitcp.pdf
+ *
+ * Unless BIC is enabled and congestion window is large
+ * this behaves the same as the original Reno.
+ */
+
+#include <linux/config.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <net/tcp.h>
+
+
+#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
+ * max_cwnd = snd_cwnd * beta
+ */
+#define BICTCP_B 4 /*
+ * In binary search,
+ * go to point (max+min)/N
+ */
+
+static int fast_convergence = 1;
+static int max_increment = 32;
+static int low_window = 14;
+static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
+static int low_utilization_threshold = 153;
+static int low_utilization_period = 2;
+static int initial_ssthresh = 100;
+static int smooth_part = 20;
+
+module_param(fast_convergence, int, 0644);
+MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
+module_param(max_increment, int, 0644);
+MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary
search");
+module_param(low_window, int, 0644);
+MODULE_PARM_DESC(low_window, "lower bound on congestion window (for TCP
friendliness)");
+module_param(beta, int, 0644);
+MODULE_PARM_DESC(beta, "beta for multiplicative increase");
+module_param(low_utilization_threshold, int, 0644);
+MODULE_PARM_DESC(low_utilization_threshold, "percent (scaled by 1024) for low
utilization mode");
+module_param(low_utilization_period, int, 0644);
+MODULE_PARM_DESC(low_utilization_period, "if average delay exceeds then goto
to low utilization mode (seconds)");
+module_param(initial_ssthresh, int, 0644);
+MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
+module_param(smooth_part, int, 0644);
+MODULE_PARM_DESC(smooth_part, "log(B/(B*Smin))/log(B/(B-1))+B, # of RTT from
Wmax-B to Wmax");
+
+
+/* BIC TCP Parameters */
+struct bictcp_ca {
+ u32 cnt; /* increase cwnd by 1 after ACKs */
+ u32 last_max_cwnd; /* last maximum snd_cwnd */
+ u32 loss_cwnd; /* congestion window at last loss */
+ u32 last_cwnd; /* the last snd_cwnd */
+ u32 last_time; /* time when updated last_cwnd */
+ u32 delay_min; /* min delay */
+ u32 delay_max; /* max delay */
+ u32 last_delay;
+ u8 low_utilization;/* 0: high; 1: low */
+ u32 low_utilization_start; /* starting time of low utilization
detection*/
+ u32 epoch_start; /* beginning of an epoch */
+};
+
+static inline void bictcp_init(struct bictcp_ca *ca)
+{
+ memset(ca, 0, sizeof(*ca));
+}
+
+static void bictcp_start(struct tcp_sock *tp)
+{
+ bictcp_init(tcp_ca(tp));
+ if (initial_ssthresh)
+ tp->snd_ssthresh = initial_ssthresh;
+}
+
+/*
+ * Compute congestion window to use.
+ */
+static inline u32 bictcp_cwnd(struct tcp_sock *tp)
+{
+ struct bictcp_ca *ca = tcp_ca(tp);
+
+ if (ca->last_cwnd == tp->snd_cwnd &&
+ (s32)(tcp_time_stamp - ca->last_time) <= (HZ>>5))
+ return ca->cnt;
+
+ ca->last_cwnd = tp->snd_cwnd;
+ ca->last_time = tcp_time_stamp;
+
+ if (ca->epoch_start == 0) /* record the beginning of an epoch */
+ ca->epoch_start = tcp_time_stamp;
+
+ /* start off normal */
+ if (tp->snd_cwnd <= low_window) {
+ ca->cnt = tp->snd_cwnd;
+ return ca->cnt;
+ }
+
+ /* binary increase */
+ if (tp->snd_cwnd < ca->last_max_cwnd) {
+ __u32 dist = (ca->last_max_cwnd - tp->snd_cwnd)
+ / BICTCP_B;
+
+ if (dist > max_increment)
+ /* linear increase */
+ ca->cnt = tp->snd_cwnd / max_increment;
+ else if (dist <= 1U)
+ /* binary search increase */
+ ca->cnt = (tp->snd_cwnd * smooth_part) / BICTCP_B;
+ else
+ /* binary search increase */
+ ca->cnt = tp->snd_cwnd / dist;
+ } else {
+ /* slow start AMD linear increase */
+ if (tp->snd_cwnd < ca->last_max_cwnd + BICTCP_B)
+ /* slow start */
+ ca->cnt = (tp->snd_cwnd * smooth_part) / BICTCP_B;
+ else if (tp->snd_cwnd < ca->last_max_cwnd +
max_increment*(BICTCP_B-1))
+ /* slow start */
+ ca->cnt = (tp->snd_cwnd * (BICTCP_B-1))
+ / tp->snd_cwnd-ca->last_max_cwnd;
+ else
+ /* linear increase */
+ ca->cnt = tp->snd_cwnd / max_increment;
+ }
+
+ /* if in slow start or link utilization is very low */
+ if ( ca->loss_cwnd == 0 ||
+ (tp->snd_cwnd > ca->loss_cwnd && ca->low_utilization)) {
+ if (ca->cnt > 20) /* increase cwnd 5% per RTT */
+ ca->cnt = 20;
+ }
+
+ ca->cnt = (ca->cnt << 3) / tp->ack_ratio;
+ if (ca->cnt == 0) /* cannot be zero */
+ ca->cnt = 1;
+
+ return ca->cnt;
+}
+
+
+/* Detect low utilization in congestion avoidance */
+static inline void bictcp_low_utilization(struct tcp_sock *tp, int flag)
+{
+ struct bictcp_ca *ca = tcp_ca(tp);
+ u32 dist, delay;
+
+ /* No time stamp */
+ if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
+ /* Discard delay samples right after fast recovery */
+ tcp_time_stamp < ca->epoch_start + HZ ||
+ /* this delay samples may not be accurate */
+ flag == 0) {
+ ca->last_delay = 0;
+ goto notlow;
+ }
+
+ delay = ca->last_delay<<3; /* use the same scale as tp->srtt*/
+ ca->last_delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
+ if (delay == 0) /* no previous delay sample */
+ goto notlow;
+
+ /* first time call or link delay decreases */
+ if (ca->delay_min == 0 || ca->delay_min > delay) {
+ ca->delay_min = ca->delay_max = delay;
+ goto notlow;
+ }
+
+ if (ca->delay_max < delay)
+ ca->delay_max = delay;
+
+ /* utilization is low, if avg delay < dist*threshold
+ for checking_period time */
+ dist = ca->delay_max - ca->delay_min;
+ if (dist <= ca->delay_min>>6 ||
+ tp->srtt - ca->delay_min >= (dist*low_utilization_threshold)>>10)
+ goto notlow;
+
+ if (ca->low_utilization_start == 0) {
+ ca->low_utilization = 0;
+ ca->low_utilization_start = tcp_time_stamp;
+ } else if (after(tcp_time_stamp,
+ ca->low_utilization_start + low_utilization_period*HZ))
+ ca->low_utilization = 1;
+
+ return;
+
+ notlow:
+ ca->low_utilization = 0;
+ ca->low_utilization_start = 0;
+
+}
+
+static void bictcp_cong_avoid(struct tcp_sock *tp, u32 ack,
+ u32 seq_rtt, u32 in_flight, int good)
+{
+ bictcp_low_utilization(tp, good);
+
+ if (in_flight < tp->snd_cwnd)
+ return;
+
+ if (tp->snd_cwnd <= tp->snd_ssthresh) {
+ /* In "safe" area, increase. */
+ if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+ tp->snd_cwnd++;
+ } else {
+ if (tp->snd_cwnd_cnt > (bictcp_cwnd(tp) << 3)) {
+ tp->snd_cwnd_cnt = 0;
+ tp->snd_cwnd++;
+ }
+ }
+
+}
+
+/*
+ * behave like Reno until low_window is reached,
+ * then increase congestion window slowly
+ */
+static u32 bictcp_recalc_ssthresh(struct tcp_sock *tp)
+{
+ struct bictcp_ca *ca = tcp_ca(tp);
+
+ ca->epoch_start = 0; /* end of epoch */
+
+ /* in case of wrong delay_max*/
+ if (ca->delay_min > 0 && ca->delay_max > ca->delay_min)
+ ca->delay_max = ca->delay_min
+ + ((ca->delay_max - ca->delay_min)* 90) / 100;
+
+ /* Wmax and fast convergence */
+ if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
+ ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
+ / (2 * BICTCP_BETA_SCALE);
+ else
+ ca->last_max_cwnd = tp->snd_cwnd;
+
+ ca->loss_cwnd = tp->snd_cwnd;
+
+ if (tp->snd_cwnd <= low_window)
+ return max(tp->snd_cwnd >> 1U, 2U);
+ else
+ return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
+}
+
+static u32 bictcp_undo_cwnd(struct tcp_sock *tp)
+{
+ struct bictcp_ca *ca = tcp_ca(tp);
+ return max(tp->snd_cwnd, ca->last_max_cwnd);
+}
+
+static void bictcp_ca_state(struct tcp_sock *tp, u8 new_state)
+{
+ if (new_state == TCP_CA_Loss)
+ bictcp_init(tcp_ca(tp));
+}
+
+static struct tcp_ca_type bictcp = {
+ .start = bictcp_start,
+ .ssthresh = bictcp_recalc_ssthresh,
+ .cong_avoid = bictcp_cong_avoid,
+ .min_cwnd = tcp_reno_cwnd_min,
+ .set_state = bictcp_ca_state,
+ .undo_cwnd = bictcp_undo_cwnd,
+
+ .owner = THIS_MODULE,
+ .name = "bic",
+};
+
+static int __init bictcp_register(void)
+{
+ BUG_ON(sizeof(struct bictcp_ca) > TCP_CA_PRIV_SIZE);
+ tcp_ca_register(&bictcp);
+ return 0;
+}
+
+static void __exit bictcp_unregister(void)
+{
+ tcp_ca_unregister(&bictcp);
+}
+
+module_init(bictcp_register);
+module_exit(bictcp_unregister);
+
+MODULE_AUTHOR("Stephen Hemminger");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("BIC TCP");
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