Merge branch 'tcp-bbr'

Neal Cardwell says:

====================
tcp: BBR congestion control algorithm

This patch series implements a new TCP congestion control algorithm:
BBR (Bottleneck Bandwidth and RTT). A paper with a detailed
description of BBR will be published in ACM Queue, September-October
2016, as "BBR: Congestion-Based Congestion Control". BBR is widely
deployed in production at Google.

The patch series starts with a set of supporting infrastructure
changes, including a few that extend the congestion control
framework. The last patch adds BBR as a TCP congestion control
module. Please see individual patches for the details.

- v3 -> v4:
 - Updated tcp_bbr.c in "tcp_bbr: add BBR congestion control"
   to use const to qualify all the constant parameters.
   Thanks to Stephen Hemminger.
 - In "tcp_bbr: add BBR congestion control", remove the bbr_rate_kbps()
   function, which had a 64-bit divide that would be problematic on some
   architectures, and just use bbr_rate_bytes_per_sec() directly.
   Thanks to Kenneth Klette Jonassen for suggesting this.
 - In "tcp: switch back to proper tcp_skb_cb size check in tcp_init()",
   switched from sizeof(skb->cb) to FIELD_SIZEOF.
   Thanks to Lance Richardson for suggesting this.
 - Updated "tcp_bbr: add BBR congestion control" commit message with
   performance data, more details about deployment at Google, and
   another reminder to use fq with BBR.
 - Updated tcp_bbr.c in "tcp_bbr: add BBR congestion control"
   to use MODULE_LICENSE("Dual BSD/GPL").

- v2 -> v3: fix another issue caught by build bots:
 - adjust rate_sample struct initialization syntax to allow gcc-4.4 to compile
   the "tcp: track data delivery rate for a TCP connection" patch; also
   adjusted some similar syntax in "tcp_bbr: add BBR congestion control"

- v1 -> v2: fix issues caught by build bots:
 - fix "tcp: export data delivery rate" to use rate64 instead of rate,
   so there is a 64-bit numerator for the do_div call
 - fix conflicting definitions for minmax caused by
   "tcp: use windowed min filter library for TCP min_rtt estimation"
   with a new commit:
   tcp: cdg: rename struct minmax in tcp_cdg.c to avoid a naming conflict
 - fix warning about the use of __packed in
   "tcp: track data delivery rate for a TCP connection",
   which involves the addition of a new commit:
   tcp: switch back to proper tcp_skb_cb size check in tcp_init()
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/tcp.h

@@ -19,6 +19,7 @@
 
 
 #include <linux/skbuff.h>
+#include <linux/win_minmax.h>
 #include <net/sock.h>
 #include <net/inet_connection_sock.h>
 #include <net/inet_timewait_sock.h>
@@ -212,7 +213,8 @@ struct tcp_sock {
 		u8 reord;    /* reordering detected */
 	} rack;
 	u16	advmss;		/* Advertised MSS			*/
-	u8	unused;
+	u8	rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */
+		unused:7;
 	u8	nonagle     : 4,/* Disable Nagle algorithm?             */
 		thin_lto    : 1,/* Use linear timeouts for thin streams */
 		thin_dupack : 1,/* Fast retransmit on first dupack      */
@@ -234,9 +236,7 @@ struct tcp_sock {
 	u32	mdev_max_us;	/* maximal mdev for the last rtt period	*/
 	u32	rttvar_us;	/* smoothed mdev_max			*/
 	u32	rtt_seq;	/* sequence number to update rttvar	*/
-	struct rtt_meas {
-		u32 rtt, ts;	/* RTT in usec and sampling time in jiffies. */
-	} rtt_min[3];
+	struct  minmax rtt_min;
 
 	u32	packets_out;	/* Packets which are "in flight"	*/
 	u32	retrans_out;	/* Retransmitted packets out		*/
@@ -268,6 +268,12 @@ struct tcp_sock {
 				 * receiver in Recovery. */
 	u32	prr_out;	/* Total number of pkts sent during Recovery. */
 	u32	delivered;	/* Total data packets delivered incl. rexmits */
+	u32	lost;		/* Total data packets lost incl. rexmits */
+	u32	app_limited;	/* limited until "delivered" reaches this val */
+	struct skb_mstamp first_tx_mstamp;  /* start of window send phase */
+	struct skb_mstamp delivered_mstamp; /* time we reached "delivered" */
+	u32	rate_delivered;    /* saved rate sample: packets delivered */
+	u32	rate_interval_us;  /* saved rate sample: time elapsed */
 
  	u32	rcv_wnd;	/* Current receiver window		*/
 	u32	write_seq;	/* Tail(+1) of data held in tcp send buffer */

include/linux/win_minmax.h

+/**
+ * lib/minmax.c: windowed min/max tracker by Kathleen Nichols.
+ *
+ */
+#ifndef MINMAX_H
+#define MINMAX_H
+
+#include <linux/types.h>
+
+/* A single data point for our parameterized min-max tracker */
+struct minmax_sample {
+	u32	t;	/* time measurement was taken */
+	u32	v;	/* value measured */
+};
+
+/* State for the parameterized min-max tracker */
+struct minmax {
+	struct minmax_sample s[3];
+};
+
+static inline u32 minmax_get(const struct minmax *m)
+{
+	return m->s[0].v;
+}
+
+static inline u32 minmax_reset(struct minmax *m, u32 t, u32 meas)
+{
+	struct minmax_sample val = { .t = t, .v = meas };
+
+	m->s[2] = m->s[1] = m->s[0] = val;
+	return m->s[0].v;
+}
+
+u32 minmax_running_max(struct minmax *m, u32 win, u32 t, u32 meas);
+u32 minmax_running_min(struct minmax *m, u32 win, u32 t, u32 meas);
+
+#endif

include/net/inet_connection_sock.h

@@ -134,8 +134,8 @@ struct inet_connection_sock {
 	} icsk_mtup;
 	u32			  icsk_user_timeout;
 
-	u64			  icsk_ca_priv[64 / sizeof(u64)];
-#define ICSK_CA_PRIV_SIZE      (8 * sizeof(u64))
+	u64			  icsk_ca_priv[88 / sizeof(u64)];
+#define ICSK_CA_PRIV_SIZE      (11 * sizeof(u64))
 };
 
 #define ICSK_TIME_RETRANS	1	/* Retransmit timer */

include/net/tcp.h

@@ -533,6 +533,8 @@ __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mss);
 #endif
 /* tcp_output.c */
 
+u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
+		     int min_tso_segs);
 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
 			       int nonagle);
 bool tcp_may_send_now(struct sock *sk);
@@ -671,7 +673,7 @@ static inline bool tcp_ca_dst_locked(const struct dst_entry *dst)
 /* Minimum RTT in usec. ~0 means not available. */
 static inline u32 tcp_min_rtt(const struct tcp_sock *tp)
 {
-	return tp->rtt_min[0].rtt;
+	return minmax_get(&tp->rtt_min);
 }
 
 /* Compute the actual receive window we are currently advertising.
@@ -763,8 +765,16 @@ struct tcp_skb_cb {
 	__u32		ack_seq;	/* Sequence number ACK'd	*/
 	union {
 		struct {
-			/* There is space for up to 20 bytes */
-			__u32 in_flight;/* Bytes in flight when packet sent */
+			/* There is space for up to 24 bytes */
+			__u32 in_flight:30,/* Bytes in flight at transmit */
+			      is_app_limited:1, /* cwnd not fully used? */
+			      unused:1;
+			/* pkts S/ACKed so far upon tx of skb, incl retrans: */
+			__u32 delivered;
+			/* start of send pipeline phase */
+			struct skb_mstamp first_tx_mstamp;
+			/* when we reached the "delivered" count */
+			struct skb_mstamp delivered_mstamp;
 		} tx;   /* only used for outgoing skbs */
 		union {
 			struct inet_skb_parm	h4;
@@ -860,6 +870,27 @@ struct ack_sample {
 	u32 in_flight;
 };
 
+/* A rate sample measures the number of (original/retransmitted) data
+ * packets delivered "delivered" over an interval of time "interval_us".
+ * The tcp_rate.c code fills in the rate sample, and congestion
+ * control modules that define a cong_control function to run at the end
+ * of ACK processing can optionally chose to consult this sample when
+ * setting cwnd and pacing rate.
+ * A sample is invalid if "delivered" or "interval_us" is negative.
+ */
+struct rate_sample {
+	struct	skb_mstamp prior_mstamp; /* starting timestamp for interval */
+	u32  prior_delivered;	/* tp->delivered at "prior_mstamp" */
+	s32  delivered;		/* number of packets delivered over interval */
+	long interval_us;	/* time for tp->delivered to incr "delivered" */
+	long rtt_us;		/* RTT of last (S)ACKed packet (or -1) */
+	int  losses;		/* number of packets marked lost upon ACK */
+	u32  acked_sacked;	/* number of packets newly (S)ACKed upon ACK */
+	u32  prior_in_flight;	/* in flight before this ACK */
+	bool is_app_limited;	/* is sample from packet with bubble in pipe? */
+	bool is_retrans;	/* is sample from retransmission? */
+};
+
 struct tcp_congestion_ops {
 	struct list_head	list;
 	u32 key;
@@ -884,6 +915,14 @@ struct tcp_congestion_ops {
 	u32  (*undo_cwnd)(struct sock *sk);
 	/* hook for packet ack accounting (optional) */
 	void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);
+	/* suggest number of segments for each skb to transmit (optional) */
+	u32 (*tso_segs_goal)(struct sock *sk);
+	/* returns the multiplier used in tcp_sndbuf_expand (optional) */
+	u32 (*sndbuf_expand)(struct sock *sk);
+	/* call when packets are delivered to update cwnd and pacing rate,
+	 * after all the ca_state processing. (optional)
+	 */
+	void (*cong_control)(struct sock *sk, const struct rate_sample *rs);
 	/* get info for inet_diag (optional) */
 	size_t (*get_info)(struct sock *sk, u32 ext, int *attr,
 			   union tcp_cc_info *info);
@@ -946,6 +985,14 @@ static inline void tcp_ca_event(struct sock *sk, const enum tcp_ca_event event)
 		icsk->icsk_ca_ops->cwnd_event(sk, event);
 }
 
+/* From tcp_rate.c */
+void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb);
+void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
+			    struct rate_sample *rs);
+void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
+		  struct skb_mstamp *now, struct rate_sample *rs);
+void tcp_rate_check_app_limited(struct sock *sk);
+
 /* These functions determine how the current flow behaves in respect of SACK
  * handling. SACK is negotiated with the peer, and therefore it can vary
  * between different flows.

include/uapi/linux/inet_diag.h

@@ -124,6 +124,7 @@ enum {
 	INET_DIAG_PEERS,
 	INET_DIAG_PAD,
 	INET_DIAG_MARK,
+	INET_DIAG_BBRINFO,
 	__INET_DIAG_MAX,
 };
 
@@ -157,8 +158,20 @@ struct tcp_dctcp_info {
 	__u32	dctcp_ab_tot;
 };
 
+/* INET_DIAG_BBRINFO */
+
+struct tcp_bbr_info {
+	/* u64 bw: max-filtered BW (app throughput) estimate in Byte per sec: */
+	__u32	bbr_bw_lo;		/* lower 32 bits of bw */
+	__u32	bbr_bw_hi;		/* upper 32 bits of bw */
+	__u32	bbr_min_rtt;		/* min-filtered RTT in uSec */
+	__u32	bbr_pacing_gain;	/* pacing gain shifted left 8 bits */
+	__u32	bbr_cwnd_gain;		/* cwnd gain shifted left 8 bits */
+};
+
 union tcp_cc_info {
 	struct tcpvegas_info	vegas;
 	struct tcp_dctcp_info	dctcp;
+	struct tcp_bbr_info	bbr;
 };
 #endif /* _UAPI_INET_DIAG_H_ */

include/uapi/linux/pkt_sched.h

@@ -792,6 +792,8 @@ enum {
 
 	TCA_FQ_ORPHAN_MASK,	/* mask applied to orphaned skb hashes */
 
+	TCA_FQ_LOW_RATE_THRESHOLD, /* per packet delay under this rate */
+
 	__TCA_FQ_MAX
 };
 

include/uapi/linux/tcp.h

@@ -167,6 +167,7 @@ struct tcp_info {
 	__u8	tcpi_backoff;
 	__u8	tcpi_options;
 	__u8	tcpi_snd_wscale : 4, tcpi_rcv_wscale : 4;
+	__u8	tcpi_delivery_rate_app_limited:1;
 
 	__u32	tcpi_rto;
 	__u32	tcpi_ato;
@@ -211,6 +212,8 @@ struct tcp_info {
 	__u32	tcpi_min_rtt;
 	__u32	tcpi_data_segs_in;	/* RFC4898 tcpEStatsDataSegsIn */
 	__u32	tcpi_data_segs_out;	/* RFC4898 tcpEStatsDataSegsOut */
+
+	__u64   tcpi_delivery_rate;
 };
 
 /* for TCP_MD5SIG socket option */

lib/Makefile

@@ -22,7 +22,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 sha1.o chacha20.o md5.o irq_regs.o argv_split.o \
 	 flex_proportions.o ratelimit.o show_mem.o \
 	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
-	 earlycpio.o seq_buf.o nmi_backtrace.o nodemask.o
+	 earlycpio.o seq_buf.o nmi_backtrace.o nodemask.o win_minmax.o
 
 lib-$(CONFIG_MMU) += ioremap.o
 lib-$(CONFIG_SMP) += cpumask.o

lib/win_minmax.c

+/**
+ * lib/minmax.c: windowed min/max tracker
+ *
+ * Kathleen Nichols' algorithm for tracking the minimum (or maximum)
+ * value of a data stream over some fixed time interval.  (E.g.,
+ * the minimum RTT over the past five minutes.) It uses constant
+ * space and constant time per update yet almost always delivers
+ * the same minimum as an implementation that has to keep all the
+ * data in the window.
+ *
+ * The algorithm keeps track of the best, 2nd best & 3rd best min
+ * values, maintaining an invariant that the measurement time of
+ * the n'th best >= n-1'th best. It also makes sure that the three
+ * values are widely separated in the time window since that bounds
+ * the worse case error when that data is monotonically increasing
+ * over the window.
+ *
+ * Upon getting a new min, we can forget everything earlier because
+ * it has no value - the new min is <= everything else in the window
+ * by definition and it's the most recent. So we restart fresh on
+ * every new min and overwrites 2nd & 3rd choices. The same property
+ * holds for 2nd & 3rd best.
+ */
+#include <linux/module.h>
+#include <linux/win_minmax.h>
+
+/* As time advances, update the 1st, 2nd, and 3rd choices. */
+static u32 minmax_subwin_update(struct minmax *m, u32 win,
+				const struct minmax_sample *val)
+{
+	u32 dt = val->t - m->s[0].t;
+
+	if (unlikely(dt > win)) {
+		/*
+		 * Passed entire window without a new val so make 2nd
+		 * choice the new val & 3rd choice the new 2nd choice.
+		 * we may have to iterate this since our 2nd choice
+		 * may also be outside the window (we checked on entry
+		 * that the third choice was in the window).
+		 */
+		m->s[0] = m->s[1];
+		m->s[1] = m->s[2];
+		m->s[2] = *val;
+		if (unlikely(val->t - m->s[0].t > win)) {
+			m->s[0] = m->s[1];
+			m->s[1] = m->s[2];
+			m->s[2] = *val;
+		}
+	} else if (unlikely(m->s[1].t == m->s[0].t) && dt > win/4) {
+		/*
+		 * We've passed a quarter of the window without a new val
+		 * so take a 2nd choice from the 2nd quarter of the window.
+		 */
+		m->s[2] = m->s[1] = *val;
+	} else if (unlikely(m->s[2].t == m->s[1].t) && dt > win/2) {
+		/*
+		 * We've passed half the window without finding a new val
+		 * so take a 3rd choice from the last half of the window
+		 */
+		m->s[2] = *val;
+	}
+	return m->s[0].v;
+}
+
+/* Check if new measurement updates the 1st, 2nd or 3rd choice max. */
+u32 minmax_running_max(struct minmax *m, u32 win, u32 t, u32 meas)
+{
+	struct minmax_sample val = { .t = t, .v = meas };
+
+	if (unlikely(val.v >= m->s[0].v) ||	  /* found new max? */
+	    unlikely(val.t - m->s[2].t > win))	  /* nothing left in window? */
+		return minmax_reset(m, t, meas);  /* forget earlier samples */
+
+	if (unlikely(val.v >= m->s[1].v))
+		m->s[2] = m->s[1] = val;
+	else if (unlikely(val.v >= m->s[2].v))
+		m->s[2] = val;
+
+	return minmax_subwin_update(m, win, &val);
+}
+EXPORT_SYMBOL(minmax_running_max);
+
+/* Check if new measurement updates the 1st, 2nd or 3rd choice min. */
+u32 minmax_running_min(struct minmax *m, u32 win, u32 t, u32 meas)
+{
+	struct minmax_sample val = { .t = t, .v = meas };
+
+	if (unlikely(val.v <= m->s[0].v) ||	  /* found new min? */
+	    unlikely(val.t - m->s[2].t > win))	  /* nothing left in window? */
+		return minmax_reset(m, t, meas);  /* forget earlier samples */
+
+	if (unlikely(val.v <= m->s[1].v))
+		m->s[2] = m->s[1] = val;
+	else if (unlikely(val.v <= m->s[2].v))
+		m->s[2] = val;
+
+	return minmax_subwin_update(m, win, &val);
+}

net/ipv4/Kconfig

@@ -640,6 +640,21 @@ config TCP_CONG_CDG
 	  D.A. Hayes and G. Armitage. "Revisiting TCP congestion control using
 	  delay gradients." In Networking 2011. Preprint: http://goo.gl/No3vdg
 
+config TCP_CONG_BBR
+	tristate "BBR TCP"
+	default n
+	---help---
+
+	BBR (Bottleneck Bandwidth and RTT) TCP congestion control aims to
+	maximize network utilization and minimize queues. It builds an explicit
+	model of the the bottleneck delivery rate and path round-trip
+	propagation delay. It tolerates packet loss and delay unrelated to
+	congestion. It can operate over LAN, WAN, cellular, wifi, or cable
+	modem links. It can coexist with flows that use loss-based congestion
+	control, and can operate with shallow buffers, deep buffers,
+	bufferbloat, policers, or AQM schemes that do not provide a delay
+	signal. It requires the fq ("Fair Queue") pacing packet scheduler.
+
 choice
 	prompt "Default TCP congestion control"
 	default DEFAULT_CUBIC
@@ -674,6 +689,9 @@ choice
 	config DEFAULT_CDG
 		bool "CDG" if TCP_CONG_CDG=y
 
+	config DEFAULT_BBR
+		bool "BBR" if TCP_CONG_BBR=y
+
 	config DEFAULT_RENO
 		bool "Reno"
 endchoice

net/ipv4/Makefile

@@ -8,7 +8,7 @@ obj-y     := route.o inetpeer.o protocol.o \
 	     inet_timewait_sock.o inet_connection_sock.o \
 	     tcp.o tcp_input.o tcp_output.o tcp_timer.o tcp_ipv4.o \
 	     tcp_minisocks.o tcp_cong.o tcp_metrics.o tcp_fastopen.o \
-	     tcp_recovery.o \
+	     tcp_rate.o tcp_recovery.o \
 	     tcp_offload.o datagram.o raw.o udp.o udplite.o \
 	     udp_offload.o arp.o icmp.o devinet.o af_inet.o igmp.o \
 	     fib_frontend.o fib_semantics.o fib_trie.o \
@@ -41,6 +41,7 @@ obj-$(CONFIG_INET_DIAG) += inet_diag.o
 obj-$(CONFIG_INET_TCP_DIAG) += tcp_diag.o
 obj-$(CONFIG_INET_UDP_DIAG) += udp_diag.o
 obj-$(CONFIG_NET_TCPPROBE) += tcp_probe.o
+obj-$(CONFIG_TCP_CONG_BBR) += tcp_bbr.o
 obj-$(CONFIG_TCP_CONG_BIC) += tcp_bic.o
 obj-$(CONFIG_TCP_CONG_CDG) += tcp_cdg.o
 obj-$(CONFIG_TCP_CONG_CUBIC) += tcp_cubic.o

net/ipv4/tcp.c

@@ -387,7 +387,7 @@ void tcp_init_sock(struct sock *sk)
 
 	icsk->icsk_rto = TCP_TIMEOUT_INIT;
 	tp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
-	tp->rtt_min[0].rtt = ~0U;
+	minmax_reset(&tp->rtt_min, tcp_time_stamp, ~0U);
 
 	/* So many TCP implementations out there (incorrectly) count the
 	 * initial SYN frame in their delayed-ACK and congestion control
@@ -396,6 +396,9 @@ void tcp_init_sock(struct sock *sk)
 	 */
 	tp->snd_cwnd = TCP_INIT_CWND;
 
+	/* There's a bubble in the pipe until at least the first ACK. */
+	tp->app_limited = ~0U;
+
 	/* See draft-stevens-tcpca-spec-01 for discussion of the
 	 * initialization of these values.
 	 */
@@ -1014,6 +1017,9 @@ int tcp_sendpage(struct sock *sk, struct page *page, int offset,
 					flags);
 
 	lock_sock(sk);
+
+	tcp_rate_check_app_limited(sk);  /* is sending application-limited? */
+
 	res = do_tcp_sendpages(sk, page, offset, size, flags);
 	release_sock(sk);
 	return res;
@@ -1115,6 +1121,8 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 
 	timeo = sock_sndtimeo(sk, flags & MSG_DONTWAIT);
 
+	tcp_rate_check_app_limited(sk);  /* is sending application-limited? */
+
 	/* Wait for a connection to finish. One exception is TCP Fast Open
 	 * (passive side) where data is allowed to be sent before a connection
 	 * is fully established.
@@ -2704,7 +2712,7 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 {
 	const struct tcp_sock *tp = tcp_sk(sk); /* iff sk_type == SOCK_STREAM */
 	const struct inet_connection_sock *icsk = inet_csk(sk);
-	u32 now = tcp_time_stamp;
+	u32 now = tcp_time_stamp, intv;
 	unsigned int start;
 	int notsent_bytes;
 	u64 rate64;
@@ -2794,6 +2802,15 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 	info->tcpi_min_rtt = tcp_min_rtt(tp);
 	info->tcpi_data_segs_in = tp->data_segs_in;
 	info->tcpi_data_segs_out = tp->data_segs_out;
+
+	info->tcpi_delivery_rate_app_limited = tp->rate_app_limited ? 1 : 0;
+	rate = READ_ONCE(tp->rate_delivered);
+	intv = READ_ONCE(tp->rate_interval_us);
+	if (rate && intv) {
+		rate64 = (u64)rate * tp->mss_cache * USEC_PER_SEC;
+		do_div(rate64, intv);
+		put_unaligned(rate64, &info->tcpi_delivery_rate);
+	}
 }
 EXPORT_SYMBOL_GPL(tcp_get_info);
 
@@ -3261,11 +3278,12 @@ static void __init tcp_init_mem(void)
 
 void __init tcp_init(void)
 {
-	unsigned long limit;
 	int max_rshare, max_wshare, cnt;
+	unsigned long limit;
 	unsigned int i;
 
-	sock_skb_cb_check_size(sizeof(struct tcp_skb_cb));
+	BUILD_BUG_ON(sizeof(struct tcp_skb_cb) >
+		     FIELD_SIZEOF(struct sk_buff, cb));
 
 	percpu_counter_init(&tcp_sockets_allocated, 0, GFP_KERNEL);
 	percpu_counter_init(&tcp_orphan_count, 0, GFP_KERNEL);

net/ipv4/tcp_cdg.c

@@ -56,7 +56,7 @@ MODULE_PARM_DESC(use_shadow, "use shadow window heuristic");
 module_param(use_tolerance, bool, 0644);
 MODULE_PARM_DESC(use_tolerance, "use loss tolerance heuristic");
 
-struct minmax {
+struct cdg_minmax {
 	union {
 		struct {
 			s32 min;
@@ -74,10 +74,10 @@ enum cdg_state {
 };
 
 struct cdg {
-	struct minmax rtt;
-	struct minmax rtt_prev;
-	struct minmax *gradients;
-	struct minmax gsum;
+	struct cdg_minmax rtt;
+	struct cdg_minmax rtt_prev;
+	struct cdg_minmax *gradients;
+	struct cdg_minmax gsum;
 	bool gfilled;
 	u8  tail;
 	u8  state;
@@ -353,7 +353,7 @@ static void tcp_cdg_cwnd_event(struct sock *sk, const enum tcp_ca_event ev)
 {
 	struct cdg *ca = inet_csk_ca(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
-	struct minmax *gradients;
+	struct cdg_minmax *gradients;
 
 	switch (ev) {
 	case CA_EVENT_CWND_RESTART:

net/ipv4/tcp_cong.c

@@ -69,7 +69,7 @@ int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
 	int ret = 0;
 
 	/* all algorithms must implement ssthresh and cong_avoid ops */
-	if (!ca->ssthresh || !ca->cong_avoid) {
+	if (!ca->ssthresh || !(ca->cong_avoid || ca->cong_control)) {
 		pr_err("%s does not implement required ops\n", ca->name);
 		return -EINVAL;
 	}

net/ipv4/tcp_minisocks.c

@@ -464,7 +464,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
 
 		newtp->srtt_us = 0;
 		newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
-		newtp->rtt_min[0].rtt = ~0U;
+		minmax_reset(&newtp->rtt_min, tcp_time_stamp, ~0U);
 		newicsk->icsk_rto = TCP_TIMEOUT_INIT;
 
 		newtp->packets_out = 0;
@@ -487,6 +487,9 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
 		newtp->snd_cwnd = TCP_INIT_CWND;
 		newtp->snd_cwnd_cnt = 0;
 
+		/* There's a bubble in the pipe until at least the first ACK. */
+		newtp->app_limited = ~0U;
+
 		tcp_init_xmit_timers(newsk);
 		newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
 

net/ipv4/tcp_output.c

@@ -918,6 +918,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
 		skb_mstamp_get(&skb->skb_mstamp);
 		TCP_SKB_CB(skb)->tx.in_flight = TCP_SKB_CB(skb)->end_seq
 			- tp->snd_una;
+		tcp_rate_skb_sent(sk, skb);
 
 		if (unlikely(skb_cloned(skb)))
 			skb = pskb_copy(skb, gfp_mask);
@@ -1213,6 +1214,9 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
 	tcp_set_skb_tso_segs(skb, mss_now);
 	tcp_set_skb_tso_segs(buff, mss_now);
 
+	/* Update delivered info for the new segment */
+	TCP_SKB_CB(buff)->tx = TCP_SKB_CB(skb)->tx;
+
 	/* If this packet has been sent out already, we must
 	 * adjust the various packet counters.
 	 */
@@ -1358,6 +1362,7 @@ int tcp_mss_to_mtu(struct sock *sk, int mss)
 	}
 	return mtu;
 }
+EXPORT_SYMBOL(tcp_mss_to_mtu);
 
 /* MTU probing init per socket */
 void tcp_mtup_init(struct sock *sk)
@@ -1545,7 +1550,8 @@ static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
 /* Return how many segs we'd like on a TSO packet,
  * to send one TSO packet per ms
  */
-static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
+u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
+		     int min_tso_segs)
 {
 	u32 bytes, segs;
 
@@ -1557,10 +1563,23 @@ static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
 	 * This preserves ACK clocking and is consistent
 	 * with tcp_tso_should_defer() heuristic.
 	 */
-	segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs);
+	segs = max_t(u32, bytes / mss_now, min_tso_segs);
 
 	return min_t(u32, segs, sk->sk_gso_max_segs);
 }
+EXPORT_SYMBOL(tcp_tso_autosize);
+
+/* Return the number of segments we want in the skb we are transmitting.
+ * See if congestion control module wants to decide; otherwise, autosize.
+ */
+static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
+{
+	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
+	u32 tso_segs = ca_ops->tso_segs_goal ? ca_ops->tso_segs_goal(sk) : 0;
+
+	return tso_segs ? :
+		tcp_tso_autosize(sk, mss_now, sysctl_tcp_min_tso_segs);
+}
 
 /* Returns the portion of skb which can be sent right away */
 static unsigned int tcp_mss_split_point(const struct sock *sk,
@@ -2057,7 +2076,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
 		}
 	}
 
-	max_segs = tcp_tso_autosize(sk, mss_now);
+	max_segs = tcp_tso_segs(sk, mss_now);
 	while ((skb = tcp_send_head(sk))) {
 		unsigned int limit;
 
@@ -2774,7 +2793,7 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
 		last_lost = tp->snd_una;
 	}
 
-	max_segs = tcp_tso_autosize(sk, tcp_current_mss(sk));
+	max_segs = tcp_tso_segs(sk, tcp_current_mss(sk));
 	tcp_for_write_queue_from(skb, sk) {
 		__u8 sacked;
 		int segs;

net/ipv4/tcp_rate.c

+#include <net/tcp.h>
+
+/* The bandwidth estimator estimates the rate at which the network
+ * can currently deliver outbound data packets for this flow. At a high
+ * level, it operates by taking a delivery rate sample for each ACK.
+ *
+ * A rate sample records the rate at which the network delivered packets
+ * for this flow, calculated over the time interval between the transmission
+ * of a data packet and the acknowledgment of that packet.
+ *
+ * Specifically, over the interval between each transmit and corresponding ACK,
+ * the estimator generates a delivery rate sample. Typically it uses the rate
+ * at which packets were acknowledged. However, the approach of using only the
+ * acknowledgment rate faces a challenge under the prevalent ACK decimation or
+ * compression: packets can temporarily appear to be delivered much quicker
+ * than the bottleneck rate. Since it is physically impossible to do that in a
+ * sustained fashion, when the estimator notices that the ACK rate is faster
+ * than the transmit rate, it uses the latter:
+ *
+ *    send_rate = #pkts_delivered/(last_snd_time - first_snd_time)
+ *    ack_rate  = #pkts_delivered/(last_ack_time - first_ack_time)
+ *    bw = min(send_rate, ack_rate)
+ *
+ * Notice the estimator essentially estimates the goodput, not always the
+ * network bottleneck link rate when the sending or receiving is limited by
+ * other factors like applications or receiver window limits.  The estimator
+ * deliberately avoids using the inter-packet spacing approach because that
+ * approach requires a large number of samples and sophisticated filtering.
+ *
+ * TCP flows can often be application-limited in request/response workloads.
+ * The estimator marks a bandwidth sample as application-limited if there
+ * was some moment during the sampled window of packets when there was no data
+ * ready to send in the write queue.
+ */
+
+/* Snapshot the current delivery information in the skb, to generate
+ * a rate sample later when the skb is (s)acked in tcp_rate_skb_delivered().
+ */
+void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	 /* In general we need to start delivery rate samples from the
+	  * time we received the most recent ACK, to ensure we include
+	  * the full time the network needs to deliver all in-flight
+	  * packets. If there are no packets in flight yet, then we
+	  * know that any ACKs after now indicate that the network was
+	  * able to deliver those packets completely in the sampling
+	  * interval between now and the next ACK.
+	  *
+	  * Note that we use packets_out instead of tcp_packets_in_flight(tp)
+	  * because the latter is a guess based on RTO and loss-marking
+	  * heuristics. We don't want spurious RTOs or loss markings to cause
+	  * a spuriously small time interval, causing a spuriously high
+	  * bandwidth estimate.
+	  */
+	if (!tp->packets_out) {
+		tp->first_tx_mstamp  = skb->skb_mstamp;
+		tp->delivered_mstamp = skb->skb_mstamp;
+	}
+
+	TCP_SKB_CB(skb)->tx.first_tx_mstamp	= tp->first_tx_mstamp;
+	TCP_SKB_CB(skb)->tx.delivered_mstamp	= tp->delivered_mstamp;
+	TCP_SKB_CB(skb)->tx.delivered		= tp->delivered;
+	TCP_SKB_CB(skb)->tx.is_app_limited	= tp->app_limited ? 1 : 0;
+}
+
+/* When an skb is sacked or acked, we fill in the rate sample with the (prior)
+ * delivery information when the skb was last transmitted.
+ *
+ * If an ACK (s)acks multiple skbs (e.g., stretched-acks), this function is
+ * called multiple times. We favor the information from the most recently
+ * sent skb, i.e., the skb with the highest prior_delivered count.
+ */
+void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
+			    struct rate_sample *rs)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
+
+	if (!scb->tx.delivered_mstamp.v64)
+		return;
+
+	if (!rs->prior_delivered ||
+	    after(scb->tx.delivered, rs->prior_delivered)) {
+		rs->prior_delivered  = scb->tx.delivered;
+		rs->prior_mstamp     = scb->tx.delivered_mstamp;
+		rs->is_app_limited   = scb->tx.is_app_limited;
+		rs->is_retrans	     = scb->sacked & TCPCB_RETRANS;
+
+		/* Find the duration of the "send phase" of this window: */
+		rs->interval_us      = skb_mstamp_us_delta(
+						&skb->skb_mstamp,
+						&scb->tx.first_tx_mstamp);
+
+		/* Record send time of most recently ACKed packet: */
+		tp->first_tx_mstamp  = skb->skb_mstamp;
+	}
+	/* Mark off the skb delivered once it's sacked to avoid being
+	 * used again when it's cumulatively acked. For acked packets
+	 * we don't need to reset since it'll be freed soon.
+	 */
+	if (scb->sacked & TCPCB_SACKED_ACKED)
+		scb->tx.delivered_mstamp.v64 = 0;
+}
+
+/* Update the connection delivery information and generate a rate sample. */
+void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
+		  struct skb_mstamp *now, struct rate_sample *rs)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	u32 snd_us, ack_us;
+
+	/* Clear app limited if bubble is acked and gone. */
+	if (tp->app_limited && after(tp->delivered, tp->app_limited))
+		tp->app_limited = 0;
+
+	/* TODO: there are multiple places throughout tcp_ack() to get
+	 * current time. Refactor the code using a new "tcp_acktag_state"
+	 * to carry current time, flags, stats like "tcp_sacktag_state".
+	 */
+	if (delivered)
+		tp->delivered_mstamp = *now;
+
+	rs->acked_sacked = delivered;	/* freshly ACKed or SACKed */
+	rs->losses = lost;		/* freshly marked lost */
+	/* Return an invalid sample if no timing information is available. */
+	if (!rs->prior_mstamp.v64) {
+		rs->delivered = -1;
+		rs->interval_us = -1;
+		return;
+	}
+	rs->delivered   = tp->delivered - rs->prior_delivered;
+
+	/* Model sending data and receiving ACKs as separate pipeline phases
+	 * for a window. Usually the ACK phase is longer, but with ACK
+	 * compression the send phase can be longer. To be safe we use the
+	 * longer phase.
+	 */
+	snd_us = rs->interval_us;				/* send phase */
+	ack_us = skb_mstamp_us_delta(now, &rs->prior_mstamp);	/* ack phase */
+	rs->interval_us = max(snd_us, ack_us);
+
+	/* Normally we expect interval_us >= min-rtt.
+	 * Note that rate may still be over-estimated when a spuriously
+	 * retransmistted skb was first (s)acked because "interval_us"
+	 * is under-estimated (up to an RTT). However continuously
+	 * measuring the delivery rate during loss recovery is crucial
+	 * for connections suffer heavy or prolonged losses.
+	 */
+	if (unlikely(rs->interval_us < tcp_min_rtt(tp))) {
+		if (!rs->is_retrans)
+			pr_debug("tcp rate: %ld %d %u %u %u\n",
+				 rs->interval_us, rs->delivered,
+				 inet_csk(sk)->icsk_ca_state,
+				 tp->rx_opt.sack_ok, tcp_min_rtt(tp));
+		rs->interval_us = -1;
+		return;
+	}
+
+	/* Record the last non-app-limited or the highest app-limited bw */
+	if (!rs->is_app_limited ||
+	    ((u64)rs->delivered * tp->rate_interval_us >=
+	     (u64)tp->rate_delivered * rs->interval_us)) {
+		tp->rate_delivered = rs->delivered;
+		tp->rate_interval_us = rs->interval_us;
+		tp->rate_app_limited = rs->is_app_limited;
+	}
+}
+
+/* If a gap is detected between sends, mark the socket application-limited. */
+void tcp_rate_check_app_limited(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (/* We have less than one packet to send. */
+	    tp->write_seq - tp->snd_nxt < tp->mss_cache &&
+	    /* Nothing in sending host's qdisc queues or NIC tx queue. */
+	    sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1) &&
+	    /* We are not limited by CWND. */
+	    tcp_packets_in_flight(tp) < tp->snd_cwnd &&
+	    /* All lost packets have been retransmitted. */
+	    tp->lost_out <= tp->retrans_out)
+		tp->app_limited =
+			(tp->delivered + tcp_packets_in_flight(tp)) ? : 1;
+}

net/sched/sch_fq.c

@@ -94,6 +94,7 @@ struct fq_sched_data {
 	u32		flow_max_rate;	/* optional max rate per flow */
 	u32		flow_plimit;	/* max packets per flow */
 	u32		orphan_mask;	/* mask for orphaned skb */
+	u32		low_rate_threshold;
 	struct rb_root	*fq_root;
 	u8		rate_enable;
 	u8		fq_trees_log;
@@ -433,7 +434,7 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
 	struct fq_flow_head *head;
 	struct sk_buff *skb;
 	struct fq_flow *f;
-	u32 rate;
+	u32 rate, plen;
 
 	skb = fq_dequeue_head(sch, &q->internal);
 	if (skb)
@@ -482,7 +483,7 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
 	prefetch(&skb->end);
 	f->credit -= qdisc_pkt_len(skb);
 
-	if (f->credit > 0 || !q->rate_enable)
+	if (!q->rate_enable)
 		goto out;
 
 	/* Do not pace locally generated ack packets */
@@ -493,8 +494,15 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
 	if (skb->sk)
 		rate = min(skb->sk->sk_pacing_rate, rate);
 
+	if (rate <= q->low_rate_threshold) {
+		f->credit = 0;
+		plen = qdisc_pkt_len(skb);
+	} else {
+		plen = max(qdisc_pkt_len(skb), q->quantum);
+		if (f->credit > 0)
+			goto out;
+	}
 	if (rate != ~0U) {
-		u32 plen = max(qdisc_pkt_len(skb), q->quantum);
 		u64 len = (u64)plen * NSEC_PER_SEC;
 
 		if (likely(rate))
@@ -662,6 +670,7 @@ static const struct nla_policy fq_policy[TCA_FQ_MAX + 1] = {
 	[TCA_FQ_FLOW_MAX_RATE]		= { .type = NLA_U32 },
 	[TCA_FQ_BUCKETS_LOG]		= { .type = NLA_U32 },
 	[TCA_FQ_FLOW_REFILL_DELAY]	= { .type = NLA_U32 },
+	[TCA_FQ_LOW_RATE_THRESHOLD]	= { .type = NLA_U32 },
 };
 
 static int fq_change(struct Qdisc *sch, struct nlattr *opt)
@@ -716,6 +725,10 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt)
 	if (tb[TCA_FQ_FLOW_MAX_RATE])
 		q->flow_max_rate = nla_get_u32(tb[TCA_FQ_FLOW_MAX_RATE]);
 
+	if (tb[TCA_FQ_LOW_RATE_THRESHOLD])
+		q->low_rate_threshold =
+			nla_get_u32(tb[TCA_FQ_LOW_RATE_THRESHOLD]);
+
 	if (tb[TCA_FQ_RATE_ENABLE]) {
 		u32 enable = nla_get_u32(tb[TCA_FQ_RATE_ENABLE]);
 
@@ -781,6 +794,7 @@ static int fq_init(struct Qdisc *sch, struct nlattr *opt)
 	q->fq_root		= NULL;
 	q->fq_trees_log		= ilog2(1024);
 	q->orphan_mask		= 1024 - 1;
+	q->low_rate_threshold	= 550000 / 8;
 	qdisc_watchdog_init(&q->watchdog, sch);
 
 	if (opt)
@@ -811,6 +825,8 @@ static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
 	    nla_put_u32(skb, TCA_FQ_FLOW_REFILL_DELAY,
 			jiffies_to_usecs(q->flow_refill_delay)) ||
 	    nla_put_u32(skb, TCA_FQ_ORPHAN_MASK, q->orphan_mask) ||
+	    nla_put_u32(skb, TCA_FQ_LOW_RATE_THRESHOLD,
+			q->low_rate_threshold) ||
 	    nla_put_u32(skb, TCA_FQ_BUCKETS_LOG, q->fq_trees_log))
 		goto nla_put_failure;