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Merge branch 'tcp-bbr'

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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>
This commit is contained in:
David S. Miller 2016-09-21 00:23:09 -04:00
commit a624f93ce6
20 changed files with 1469 additions and 106 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
include/linux/tcp.h
View File

@ -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 */

37
include/linux/win_minmax.h Normal file
View File

@ -0,0 +1,37 @@
/**
* 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

4
include/net/inet_connection_sock.h
View File

@ -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 */

53
include/net/tcp.h
View File

@ -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.

13
include/uapi/linux/inet_diag.h
View File

@ -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_ */

2
include/uapi/linux/pkt_sched.h
View File

@ -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
};

3
include/uapi/linux/tcp.h
View File

@ -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 */

2
lib/Makefile
View File

@ -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

98
lib/win_minmax.c Normal file
View File

@ -0,0 +1,98 @@
/**
* 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);
}

18
net/ipv4/Kconfig
View File

@ -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

3
net/ipv4/Makefile
View File

@ -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

26
net/ipv4/tcp.c
View File

@ -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);

896
net/ipv4/tcp_bbr.c Normal file
View File

@ -0,0 +1,896 @@
/* Bottleneck Bandwidth and RTT (BBR) congestion control
*
* BBR congestion control computes the sending rate based on the delivery
* rate (throughput) estimated from ACKs. In a nutshell:
*
* On each ACK, update our model of the network path:
* bottleneck_bandwidth = windowed_max(delivered / elapsed, 10 round trips)
* min_rtt = windowed_min(rtt, 10 seconds)
* pacing_rate = pacing_gain * bottleneck_bandwidth
* cwnd = max(cwnd_gain * bottleneck_bandwidth * min_rtt, 4)
*
* The core algorithm does not react directly to packet losses or delays,
* although BBR may adjust the size of next send per ACK when loss is
* observed, or adjust the sending rate if it estimates there is a
* traffic policer, in order to keep the drop rate reasonable.
*
* BBR is described in detail in:
* "BBR: Congestion-Based Congestion Control",
* Neal Cardwell, Yuchung Cheng, C. Stephen Gunn, Soheil Hassas Yeganeh,
* Van Jacobson. ACM Queue, Vol. 14 No. 5, September-October 2016.
*
* There is a public e-mail list for discussing BBR development and testing:
* https://groups.google.com/forum/#!forum/bbr-dev
*
* NOTE: BBR *must* be used with the fq qdisc ("man tc-fq") with pacing enabled,
* since pacing is integral to the BBR design and implementation.
* BBR without pacing would not function properly, and may incur unnecessary
* high packet loss rates.
*/
#include <linux/module.h>
#include <net/tcp.h>
#include <linux/inet_diag.h>
#include <linux/inet.h>
#include <linux/random.h>
#include <linux/win_minmax.h>
/* Scale factor for rate in pkt/uSec unit to avoid truncation in bandwidth
* estimation. The rate unit ~= (1500 bytes / 1 usec / 2^24) ~= 715 bps.
* This handles bandwidths from 0.06pps (715bps) to 256Mpps (3Tbps) in a u32.
* Since the minimum window is >=4 packets, the lower bound isn't
* an issue. The upper bound isn't an issue with existing technologies.
*/
#define BW_SCALE 24
#define BW_UNIT (1 << BW_SCALE)
#define BBR_SCALE 8 /* scaling factor for fractions in BBR (e.g. gains) */
#define BBR_UNIT (1 << BBR_SCALE)
/* BBR has the following modes for deciding how fast to send: */
enum bbr_mode {
BBR_STARTUP, /* ramp up sending rate rapidly to fill pipe */
BBR_DRAIN, /* drain any queue created during startup */
BBR_PROBE_BW, /* discover, share bw: pace around estimated bw */
BBR_PROBE_RTT, /* cut cwnd to min to probe min_rtt */
};
/* BBR congestion control block */
struct bbr {
u32 min_rtt_us; /* min RTT in min_rtt_win_sec window */
u32 min_rtt_stamp; /* timestamp of min_rtt_us */
u32 probe_rtt_done_stamp; /* end time for BBR_PROBE_RTT mode */
struct minmax bw; /* Max recent delivery rate in pkts/uS << 24 */
u32 rtt_cnt; /* count of packet-timed rounds elapsed */
u32 next_rtt_delivered; /* scb->tx.delivered at end of round */
struct skb_mstamp cycle_mstamp; /* time of this cycle phase start */
u32 mode:3, /* current bbr_mode in state machine */
prev_ca_state:3, /* CA state on previous ACK */
packet_conservation:1, /* use packet conservation? */
restore_cwnd:1, /* decided to revert cwnd to old value */
round_start:1, /* start of packet-timed tx->ack round? */
tso_segs_goal:7, /* segments we want in each skb we send */
idle_restart:1, /* restarting after idle? */
probe_rtt_round_done:1, /* a BBR_PROBE_RTT round at 4 pkts? */
unused:5,
lt_is_sampling:1, /* taking long-term ("LT") samples now? */
lt_rtt_cnt:7, /* round trips in long-term interval */
lt_use_bw:1; /* use lt_bw as our bw estimate? */
u32 lt_bw; /* LT est delivery rate in pkts/uS << 24 */
u32 lt_last_delivered; /* LT intvl start: tp->delivered */
u32 lt_last_stamp; /* LT intvl start: tp->delivered_mstamp */
u32 lt_last_lost; /* LT intvl start: tp->lost */
u32 pacing_gain:10, /* current gain for setting pacing rate */
cwnd_gain:10, /* current gain for setting cwnd */
full_bw_cnt:3, /* number of rounds without large bw gains */
cycle_idx:3, /* current index in pacing_gain cycle array */
unused_b:6;
u32 prior_cwnd; /* prior cwnd upon entering loss recovery */
u32 full_bw; /* recent bw, to estimate if pipe is full */
};
#define CYCLE_LEN 8 /* number of phases in a pacing gain cycle */
/* Window length of bw filter (in rounds): */
static const int bbr_bw_rtts = CYCLE_LEN + 2;
/* Window length of min_rtt filter (in sec): */
static const u32 bbr_min_rtt_win_sec = 10;
/* Minimum time (in ms) spent at bbr_cwnd_min_target in BBR_PROBE_RTT mode: */
static const u32 bbr_probe_rtt_mode_ms = 200;
/* Skip TSO below the following bandwidth (bits/sec): */
static const int bbr_min_tso_rate = 1200000;
/* We use a high_gain value of 2/ln(2) because it's the smallest pacing gain
* that will allow a smoothly increasing pacing rate that will double each RTT
* and send the same number of packets per RTT that an un-paced, slow-starting
* Reno or CUBIC flow would:
*/
static const int bbr_high_gain = BBR_UNIT * 2885 / 1000 + 1;
/* The pacing gain of 1/high_gain in BBR_DRAIN is calculated to typically drain
* the queue created in BBR_STARTUP in a single round:
*/
static const int bbr_drain_gain = BBR_UNIT * 1000 / 2885;
/* The gain for deriving steady-state cwnd tolerates delayed/stretched ACKs: */
static const int bbr_cwnd_gain = BBR_UNIT * 2;
/* The pacing_gain values for the PROBE_BW gain cycle, to discover/share bw: */
static const int bbr_pacing_gain[] = {
BBR_UNIT * 5 / 4, /* probe for more available bw */
BBR_UNIT * 3 / 4, /* drain queue and/or yield bw to other flows */
BBR_UNIT, BBR_UNIT, BBR_UNIT, /* cruise at 1.0*bw to utilize pipe, */
BBR_UNIT, BBR_UNIT, BBR_UNIT /* without creating excess queue... */
};
/* Randomize the starting gain cycling phase over N phases: */
static const u32 bbr_cycle_rand = 7;
/* Try to keep at least this many packets in flight, if things go smoothly. For
* smooth functioning, a sliding window protocol ACKing every other packet
* needs at least 4 packets in flight:
*/
static const u32 bbr_cwnd_min_target = 4;
/* To estimate if BBR_STARTUP mode (i.e. high_gain) has filled pipe... */
/* If bw has increased significantly (1.25x), there may be more bw available: */
static const u32 bbr_full_bw_thresh = BBR_UNIT * 5 / 4;
/* But after 3 rounds w/o significant bw growth, estimate pipe is full: */
static const u32 bbr_full_bw_cnt = 3;
/* "long-term" ("LT") bandwidth estimator parameters... */
/* The minimum number of rounds in an LT bw sampling interval: */
static const u32 bbr_lt_intvl_min_rtts = 4;
/* If lost/delivered ratio > 20%, interval is "lossy" and we may be policed: */
static const u32 bbr_lt_loss_thresh = 50;
/* If 2 intervals have a bw ratio <= 1/8, their bw is "consistent": */
static const u32 bbr_lt_bw_ratio = BBR_UNIT / 8;
/* If 2 intervals have a bw diff <= 4 Kbit/sec their bw is "consistent": */
static const u32 bbr_lt_bw_diff = 4000 / 8;
/* If we estimate we're policed, use lt_bw for this many round trips: */
static const u32 bbr_lt_bw_max_rtts = 48;
/* Do we estimate that STARTUP filled the pipe? */
static bool bbr_full_bw_reached(const struct sock *sk)
{
const struct bbr *bbr = inet_csk_ca(sk);
return bbr->full_bw_cnt >= bbr_full_bw_cnt;
}
/* Return the windowed max recent bandwidth sample, in pkts/uS << BW_SCALE. */
static u32 bbr_max_bw(const struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
return minmax_get(&bbr->bw);
}
/* Return the estimated bandwidth of the path, in pkts/uS << BW_SCALE. */
static u32 bbr_bw(const struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
return bbr->lt_use_bw ? bbr->lt_bw : bbr_max_bw(sk);
}
/* Return rate in bytes per second, optionally with a gain.
* The order here is chosen carefully to avoid overflow of u64. This should
* work for input rates of up to 2.9Tbit/sec and gain of 2.89x.
*/
static u64 bbr_rate_bytes_per_sec(struct sock *sk, u64 rate, int gain)
{
rate *= tcp_mss_to_mtu(sk, tcp_sk(sk)->mss_cache);
rate *= gain;
rate >>= BBR_SCALE;
rate *= USEC_PER_SEC;
return rate >> BW_SCALE;
}
/* Pace using current bw estimate and a gain factor. In order to help drive the
* network toward lower queues while maintaining high utilization and low
* latency, the average pacing rate aims to be slightly (~1%) lower than the
* estimated bandwidth. This is an important aspect of the design. In this
* implementation this slightly lower pacing rate is achieved implicitly by not
* including link-layer headers in the packet size used for the pacing rate.
*/
static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)
{
struct bbr *bbr = inet_csk_ca(sk);
u64 rate = bw;
rate = bbr_rate_bytes_per_sec(sk, rate, gain);
rate = min_t(u64, rate, sk->sk_max_pacing_rate);
if (bbr->mode != BBR_STARTUP || rate > sk->sk_pacing_rate)
sk->sk_pacing_rate = rate;
}
/* Return count of segments we want in the skbs we send, or 0 for default. */
static u32 bbr_tso_segs_goal(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
return bbr->tso_segs_goal;
}
static void bbr_set_tso_segs_goal(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u32 min_segs;
min_segs = sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;
bbr->tso_segs_goal = min(tcp_tso_autosize(sk, tp->mss_cache, min_segs),
0x7FU);
}
/* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */
static void bbr_save_cwnd(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
if (bbr->prev_ca_state < TCP_CA_Recovery && bbr->mode != BBR_PROBE_RTT)
bbr->prior_cwnd = tp->snd_cwnd; /* this cwnd is good enough */
else /* loss recovery or BBR_PROBE_RTT have temporarily cut cwnd */
bbr->prior_cwnd = max(bbr->prior_cwnd, tp->snd_cwnd);
}
static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
if (event == CA_EVENT_TX_START && tp->app_limited) {
bbr->idle_restart = 1;
/* Avoid pointless buffer overflows: pace at est. bw if we don't
* need more speed (we're restarting from idle and app-limited).
*/
if (bbr->mode == BBR_PROBE_BW)
bbr_set_pacing_rate(sk, bbr_bw(sk), BBR_UNIT);
}
}
/* Find target cwnd. Right-size the cwnd based on min RTT and the
* estimated bottleneck bandwidth:
*
* cwnd = bw * min_rtt * gain = BDP * gain
*
* The key factor, gain, controls the amount of queue. While a small gain
* builds a smaller queue, it becomes more vulnerable to noise in RTT
* measurements (e.g., delayed ACKs or other ACK compression effects). This
* noise may cause BBR to under-estimate the rate.
*
* To achieve full performance in high-speed paths, we budget enough cwnd to
* fit full-sized skbs in-flight on both end hosts to fully utilize the path:
* - one skb in sending host Qdisc,
* - one skb in sending host TSO/GSO engine
* - one skb being received by receiver host LRO/GRO/delayed-ACK engine
* Don't worry, at low rates (bbr_min_tso_rate) this won't bloat cwnd because
* in such cases tso_segs_goal is 1. The minimum cwnd is 4 packets,
* which allows 2 outstanding 2-packet sequences, to try to keep pipe
* full even with ACK-every-other-packet delayed ACKs.
*/
static u32 bbr_target_cwnd(struct sock *sk, u32 bw, int gain)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 cwnd;
u64 w;
/* If we've never had a valid RTT sample, cap cwnd at the initial
* default. This should only happen when the connection is not using TCP
* timestamps and has retransmitted all of the SYN/SYNACK/data packets
* ACKed so far. In this case, an RTO can cut cwnd to 1, in which
* case we need to slow-start up toward something safe: TCP_INIT_CWND.
*/
if (unlikely(bbr->min_rtt_us == ~0U)) /* no valid RTT samples yet? */
return TCP_INIT_CWND; /* be safe: cap at default initial cwnd*/
w = (u64)bw * bbr->min_rtt_us;
/* Apply a gain to the given value, then remove the BW_SCALE shift. */
cwnd = (((w * gain) >> BBR_SCALE) + BW_UNIT - 1) / BW_UNIT;
/* Allow enough full-sized skbs in flight to utilize end systems. */
cwnd += 3 * bbr->tso_segs_goal;
/* Reduce delayed ACKs by rounding up cwnd to the next even number. */
cwnd = (cwnd + 1) & ~1U;
return cwnd;
}
/* An optimization in BBR to reduce losses: On the first round of recovery, we
* follow the packet conservation principle: send P packets per P packets acked.
* After that, we slow-start and send at most 2*P packets per P packets acked.
* After recovery finishes, or upon undo, we restore the cwnd we had when
* recovery started (capped by the target cwnd based on estimated BDP).
*
* TODO(ycheng/ncardwell): implement a rate-based approach.
*/
static bool bbr_set_cwnd_to_recover_or_restore(
struct sock *sk, const struct rate_sample *rs, u32 acked, u32 *new_cwnd)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u8 prev_state = bbr->prev_ca_state, state = inet_csk(sk)->icsk_ca_state;
u32 cwnd = tp->snd_cwnd;
/* An ACK for P pkts should release at most 2*P packets. We do this
* in two steps. First, here we deduct the number of lost packets.
* Then, in bbr_set_cwnd() we slow start up toward the target cwnd.
*/
if (rs->losses > 0)
cwnd = max_t(s32, cwnd - rs->losses, 1);
if (state == TCP_CA_Recovery && prev_state != TCP_CA_Recovery) {
/* Starting 1st round of Recovery, so do packet conservation. */
bbr->packet_conservation = 1;
bbr->next_rtt_delivered = tp->delivered; /* start round now */
/* Cut unused cwnd from app behavior, TSQ, or TSO deferral: */
cwnd = tcp_packets_in_flight(tp) + acked;
} else if (prev_state >= TCP_CA_Recovery && state < TCP_CA_Recovery) {
/* Exiting loss recovery; restore cwnd saved before recovery. */
bbr->restore_cwnd = 1;
bbr->packet_conservation = 0;
}
bbr->prev_ca_state = state;
if (bbr->restore_cwnd) {
/* Restore cwnd after exiting loss recovery or PROBE_RTT. */
cwnd = max(cwnd, bbr->prior_cwnd);
bbr->restore_cwnd = 0;
}
if (bbr->packet_conservation) {
*new_cwnd = max(cwnd, tcp_packets_in_flight(tp) + acked);
return true; /* yes, using packet conservation */
}
*new_cwnd = cwnd;
return false;
}
/* Slow-start up toward target cwnd (if bw estimate is growing, or packet loss
* has drawn us down below target), or snap down to target if we're above it.
*/
static void bbr_set_cwnd(struct sock *sk, const struct rate_sample *rs,
u32 acked, u32 bw, int gain)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u32 cwnd = 0, target_cwnd = 0;
if (!acked)
return;
if (bbr_set_cwnd_to_recover_or_restore(sk, rs, acked, &cwnd))
goto done;
/* If we're below target cwnd, slow start cwnd toward target cwnd. */
target_cwnd = bbr_target_cwnd(sk, bw, gain);
if (bbr_full_bw_reached(sk)) /* only cut cwnd if we filled the pipe */
cwnd = min(cwnd + acked, target_cwnd);
else if (cwnd < target_cwnd || tp->delivered < TCP_INIT_CWND)
cwnd = cwnd + acked;
cwnd = max(cwnd, bbr_cwnd_min_target);
done:
tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp); /* apply global cap */
if (bbr->mode == BBR_PROBE_RTT) /* drain queue, refresh min_rtt */
tp->snd_cwnd = min(tp->snd_cwnd, bbr_cwnd_min_target);
}
/* End cycle phase if it's time and/or we hit the phase's in-flight target. */
static bool bbr_is_next_cycle_phase(struct sock *sk,
const struct rate_sample *rs)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bool is_full_length =
skb_mstamp_us_delta(&tp->delivered_mstamp, &bbr->cycle_mstamp) >
bbr->min_rtt_us;
u32 inflight, bw;
/* The pacing_gain of 1.0 paces at the estimated bw to try to fully
* use the pipe without increasing the queue.
*/
if (bbr->pacing_gain == BBR_UNIT)
return is_full_length; /* just use wall clock time */
inflight = rs->prior_in_flight; /* what was in-flight before ACK? */
bw = bbr_max_bw(sk);
/* A pacing_gain > 1.0 probes for bw by trying to raise inflight to at
* least pacing_gain*BDP; this may take more than min_rtt if min_rtt is
* small (e.g. on a LAN). We do not persist if packets are lost, since
* a path with small buffers may not hold that much.
*/
if (bbr->pacing_gain > BBR_UNIT)
return is_full_length &&
(rs->losses || /* perhaps pacing_gain*BDP won't fit */
inflight >= bbr_target_cwnd(sk, bw, bbr->pacing_gain));
/* A pacing_gain < 1.0 tries to drain extra queue we added if bw
* probing didn't find more bw. If inflight falls to match BDP then we
* estimate queue is drained; persisting would underutilize the pipe.
*/
return is_full_length ||
inflight <= bbr_target_cwnd(sk, bw, BBR_UNIT);
}
static void bbr_advance_cycle_phase(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bbr->cycle_idx = (bbr->cycle_idx + 1) & (CYCLE_LEN - 1);
bbr->cycle_mstamp = tp->delivered_mstamp;
bbr->pacing_gain = bbr_pacing_gain[bbr->cycle_idx];
}
/* Gain cycling: cycle pacing gain to converge to fair share of available bw. */
static void bbr_update_cycle_phase(struct sock *sk,
const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
if ((bbr->mode == BBR_PROBE_BW) && !bbr->lt_use_bw &&
bbr_is_next_cycle_phase(sk, rs))
bbr_advance_cycle_phase(sk);
}
static void bbr_reset_startup_mode(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr->mode = BBR_STARTUP;
bbr->pacing_gain = bbr_high_gain;
bbr->cwnd_gain = bbr_high_gain;
}
static void bbr_reset_probe_bw_mode(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr->mode = BBR_PROBE_BW;
bbr->pacing_gain = BBR_UNIT;
bbr->cwnd_gain = bbr_cwnd_gain;
bbr->cycle_idx = CYCLE_LEN - 1 - prandom_u32_max(bbr_cycle_rand);
bbr_advance_cycle_phase(sk); /* flip to next phase of gain cycle */
}
static void bbr_reset_mode(struct sock *sk)
{
if (!bbr_full_bw_reached(sk))
bbr_reset_startup_mode(sk);
else
bbr_reset_probe_bw_mode(sk);
}
/* Start a new long-term sampling interval. */
static void bbr_reset_lt_bw_sampling_interval(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bbr->lt_last_stamp = tp->delivered_mstamp.stamp_jiffies;
bbr->lt_last_delivered = tp->delivered;
bbr->lt_last_lost = tp->lost;
bbr->lt_rtt_cnt = 0;
}
/* Completely reset long-term bandwidth sampling. */
static void bbr_reset_lt_bw_sampling(struct sock *sk)
{
struct bbr *bbr = inet_csk_ca(sk);
bbr->lt_bw = 0;
bbr->lt_use_bw = 0;
bbr->lt_is_sampling = false;
bbr_reset_lt_bw_sampling_interval(sk);
}
/* Long-term bw sampling interval is done. Estimate whether we're policed. */
static void bbr_lt_bw_interval_done(struct sock *sk, u32 bw)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 diff;
if (bbr->lt_bw) { /* do we have bw from a previous interval? */
/* Is new bw close to the lt_bw from the previous interval? */
diff = abs(bw - bbr->lt_bw);
if ((diff * BBR_UNIT <= bbr_lt_bw_ratio * bbr->lt_bw) ||
(bbr_rate_bytes_per_sec(sk, diff, BBR_UNIT) <=
bbr_lt_bw_diff)) {
/* All criteria are met; estimate we're policed. */
bbr->lt_bw = (bw + bbr->lt_bw) >> 1; /* avg 2 intvls */
bbr->lt_use_bw = 1;
bbr->pacing_gain = BBR_UNIT; /* try to avoid drops */
bbr->lt_rtt_cnt = 0;
return;
}
}
bbr->lt_bw = bw;
bbr_reset_lt_bw_sampling_interval(sk);
}
/* Token-bucket traffic policers are common (see "An Internet-Wide Analysis of
* Traffic Policing", SIGCOMM 2016). BBR detects token-bucket policers and
* explicitly models their policed rate, to reduce unnecessary losses. We
* estimate that we're policed if we see 2 consecutive sampling intervals with
* consistent throughput and high packet loss. If we think we're being policed,
* set lt_bw to the "long-term" average delivery rate from those 2 intervals.
*/
static void bbr_lt_bw_sampling(struct sock *sk, const struct rate_sample *rs)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u32 lost, delivered;
u64 bw;
s32 t;
if (bbr->lt_use_bw) { /* already using long-term rate, lt_bw? */
if (bbr->mode == BBR_PROBE_BW && bbr->round_start &&
++bbr->lt_rtt_cnt >= bbr_lt_bw_max_rtts) {
bbr_reset_lt_bw_sampling(sk); /* stop using lt_bw */
bbr_reset_probe_bw_mode(sk); /* restart gain cycling */
}
return;
}
/* Wait for the first loss before sampling, to let the policer exhaust
* its tokens and estimate the steady-state rate allowed by the policer.
* Starting samples earlier includes bursts that over-estimate the bw.
*/
if (!bbr->lt_is_sampling) {
if (!rs->losses)
return;
bbr_reset_lt_bw_sampling_interval(sk);
bbr->lt_is_sampling = true;
}
/* To avoid underestimates, reset sampling if we run out of data. */
if (rs->is_app_limited) {
bbr_reset_lt_bw_sampling(sk);
return;
}
if (bbr->round_start)
bbr->lt_rtt_cnt++; /* count round trips in this interval */
if (bbr->lt_rtt_cnt < bbr_lt_intvl_min_rtts)
return; /* sampling interval needs to be longer */
if (bbr->lt_rtt_cnt > 4 * bbr_lt_intvl_min_rtts) {
bbr_reset_lt_bw_sampling(sk); /* interval is too long */
return;
}
/* End sampling interval when a packet is lost, so we estimate the
* policer tokens were exhausted. Stopping the sampling before the
* tokens are exhausted under-estimates the policed rate.
*/
if (!rs->losses)
return;
/* Calculate packets lost and delivered in sampling interval. */
lost = tp->lost - bbr->lt_last_lost;
delivered = tp->delivered - bbr->lt_last_delivered;
/* Is loss rate (lost/delivered) >= lt_loss_thresh? If not, wait. */
if (!delivered || (lost << BBR_SCALE) < bbr_lt_loss_thresh * delivered)
return;
/* Find average delivery rate in this sampling interval. */
t = (s32)(tp->delivered_mstamp.stamp_jiffies - bbr->lt_last_stamp);
if (t < 1)
return; /* interval is less than one jiffy, so wait */
t = jiffies_to_usecs(t);
/* Interval long enough for jiffies_to_usecs() to return a bogus 0? */
if (t < 1) {
bbr_reset_lt_bw_sampling(sk); /* interval too long; reset */
return;
}
bw = (u64)delivered * BW_UNIT;
do_div(bw, t);
bbr_lt_bw_interval_done(sk, bw);
}
/* Estimate the bandwidth based on how fast packets are delivered */
static void bbr_update_bw(struct sock *sk, const struct rate_sample *rs)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u64 bw;
bbr->round_start = 0;
if (rs->delivered < 0 || rs->interval_us <= 0)
return; /* Not a valid observation */
/* See if we've reached the next RTT */
if (!before(rs->prior_delivered, bbr->next_rtt_delivered)) {
bbr->next_rtt_delivered = tp->delivered;
bbr->rtt_cnt++;
bbr->round_start = 1;
bbr->packet_conservation = 0;
}
bbr_lt_bw_sampling(sk, rs);
/* Divide delivered by the interval to find a (lower bound) bottleneck
* bandwidth sample. Delivered is in packets and interval_us in uS and
* ratio will be <<1 for most connections. So delivered is first scaled.
*/
bw = (u64)rs->delivered * BW_UNIT;
do_div(bw, rs->interval_us);
/* If this sample is application-limited, it is likely to have a very
* low delivered count that represents application behavior rather than
* the available network rate. Such a sample could drag down estimated
* bw, causing needless slow-down. Thus, to continue to send at the
* last measured network rate, we filter out app-limited samples unless
* they describe the path bw at least as well as our bw model.
*
* So the goal during app-limited phase is to proceed with the best
* network rate no matter how long. We automatically leave this
* phase when app writes faster than the network can deliver :)
*/
if (!rs->is_app_limited || bw >= bbr_max_bw(sk)) {
/* Incorporate new sample into our max bw filter. */
minmax_running_max(&bbr->bw, bbr_bw_rtts, bbr->rtt_cnt, bw);
}
}
/* Estimate when the pipe is full, using the change in delivery rate: BBR
* estimates that STARTUP filled the pipe if the estimated bw hasn't changed by
* at least bbr_full_bw_thresh (25%) after bbr_full_bw_cnt (3) non-app-limited
* rounds. Why 3 rounds: 1: rwin autotuning grows the rwin, 2: we fill the
* higher rwin, 3: we get higher delivery rate samples. Or transient
* cross-traffic or radio noise can go away. CUBIC Hystart shares a similar
* design goal, but uses delay and inter-ACK spacing instead of bandwidth.
*/
static void bbr_check_full_bw_reached(struct sock *sk,
const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 bw_thresh;
if (bbr_full_bw_reached(sk) || !bbr->round_start || rs->is_app_limited)
return;
bw_thresh = (u64)bbr->full_bw * bbr_full_bw_thresh >> BBR_SCALE;
if (bbr_max_bw(sk) >= bw_thresh) {
bbr->full_bw = bbr_max_bw(sk);
bbr->full_bw_cnt = 0;
return;
}
++bbr->full_bw_cnt;
}
/* If pipe is probably full, drain the queue and then enter steady-state. */
static void bbr_check_drain(struct sock *sk, const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
if (bbr->mode == BBR_STARTUP && bbr_full_bw_reached(sk)) {
bbr->mode = BBR_DRAIN; /* drain queue we created */
bbr->pacing_gain = bbr_drain_gain; /* pace slow to drain */
bbr->cwnd_gain = bbr_high_gain; /* maintain cwnd */
} /* fall through to check if in-flight is already small: */
if (bbr->mode == BBR_DRAIN &&
tcp_packets_in_flight(tcp_sk(sk)) <=
bbr_target_cwnd(sk, bbr_max_bw(sk), BBR_UNIT))
bbr_reset_probe_bw_mode(sk); /* we estimate queue is drained */
}
/* The goal of PROBE_RTT mode is to have BBR flows cooperatively and
* periodically drain the bottleneck queue, to converge to measure the true
* min_rtt (unloaded propagation delay). This allows the flows to keep queues
* small (reducing queuing delay and packet loss) and achieve fairness among
* BBR flows.
*
* The min_rtt filter window is 10 seconds. When the min_rtt estimate expires,
* we enter PROBE_RTT mode and cap the cwnd at bbr_cwnd_min_target=4 packets.
* After at least bbr_probe_rtt_mode_ms=200ms and at least one packet-timed
* round trip elapsed with that flight size <= 4, we leave PROBE_RTT mode and
* re-enter the previous mode. BBR uses 200ms to approximately bound the
* performance penalty of PROBE_RTT's cwnd capping to roughly 2% (200ms/10s).
*
* Note that flows need only pay 2% if they are busy sending over the last 10
* seconds. Interactive applications (e.g., Web, RPCs, video chunks) often have
* natural silences or low-rate periods within 10 seconds where the rate is low
* enough for long enough to drain its queue in the bottleneck. We pick up
* these min RTT measurements opportunistically with our min_rtt filter. :-)
*/
static void bbr_update_min_rtt(struct sock *sk, const struct rate_sample *rs)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bool filter_expired;
/* Track min RTT seen in the min_rtt_win_sec filter window: */
filter_expired = after(tcp_time_stamp,
bbr->min_rtt_stamp + bbr_min_rtt_win_sec * HZ);
if (rs->rtt_us >= 0 &&
(rs->rtt_us <= bbr->min_rtt_us || filter_expired)) {
bbr->min_rtt_us = rs->rtt_us;
bbr->min_rtt_stamp = tcp_time_stamp;
}
if (bbr_probe_rtt_mode_ms > 0 && filter_expired &&
!bbr->idle_restart && bbr->mode != BBR_PROBE_RTT) {
bbr->mode = BBR_PROBE_RTT; /* dip, drain queue */
bbr->pacing_gain = BBR_UNIT;
bbr->cwnd_gain = BBR_UNIT;
bbr_save_cwnd(sk); /* note cwnd so we can restore it */
bbr->probe_rtt_done_stamp = 0;
}
if (bbr->mode == BBR_PROBE_RTT) {
/* Ignore low rate samples during this mode. */
tp->app_limited =
(tp->delivered + tcp_packets_in_flight(tp)) ? : 1;
/* Maintain min packets in flight for max(200 ms, 1 round). */
if (!bbr->probe_rtt_done_stamp &&
tcp_packets_in_flight(tp) <= bbr_cwnd_min_target) {
bbr->probe_rtt_done_stamp = tcp_time_stamp +
msecs_to_jiffies(bbr_probe_rtt_mode_ms);
bbr->probe_rtt_round_done = 0;
bbr->next_rtt_delivered = tp->delivered;
} else if (bbr->probe_rtt_done_stamp) {
if (bbr->round_start)
bbr->probe_rtt_round_done = 1;
if (bbr->probe_rtt_round_done &&
after(tcp_time_stamp, bbr->probe_rtt_done_stamp)) {
bbr->min_rtt_stamp = tcp_time_stamp;
bbr->restore_cwnd = 1; /* snap to prior_cwnd */
bbr_reset_mode(sk);
}
}
}
bbr->idle_restart = 0;
}
static void bbr_update_model(struct sock *sk, const struct rate_sample *rs)
{
bbr_update_bw(sk, rs);
bbr_update_cycle_phase(sk, rs);
bbr_check_full_bw_reached(sk, rs);
bbr_check_drain(sk, rs);
bbr_update_min_rtt(sk, rs);
}
static void bbr_main(struct sock *sk, const struct rate_sample *rs)
{
struct bbr *bbr = inet_csk_ca(sk);
u32 bw;
bbr_update_model(sk, rs);
bw = bbr_bw(sk);
bbr_set_pacing_rate(sk, bw, bbr->pacing_gain);
bbr_set_tso_segs_goal(sk);
bbr_set_cwnd(sk, rs, rs->acked_sacked, bw, bbr->cwnd_gain);
}
static void bbr_init(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u64 bw;
bbr->prior_cwnd = 0;
bbr->tso_segs_goal = 0; /* default segs per skb until first ACK */
bbr->rtt_cnt = 0;
bbr->next_rtt_delivered = 0;
bbr->prev_ca_state = TCP_CA_Open;
bbr->packet_conservation = 0;
bbr->probe_rtt_done_stamp = 0;
bbr->probe_rtt_round_done = 0;
bbr->min_rtt_us = tcp_min_rtt(tp);
bbr->min_rtt_stamp = tcp_time_stamp;
minmax_reset(&bbr->bw, bbr->rtt_cnt, 0); /* init max bw to 0 */
/* Initialize pacing rate to: high_gain * init_cwnd / RTT. */
bw = (u64)tp->snd_cwnd * BW_UNIT;
do_div(bw, (tp->srtt_us >> 3) ? : USEC_PER_MSEC);
sk->sk_pacing_rate = 0; /* force an update of sk_pacing_rate */
bbr_set_pacing_rate(sk, bw, bbr_high_gain);
bbr->restore_cwnd = 0;
bbr->round_start = 0;
bbr->idle_restart = 0;
bbr->full_bw = 0;
bbr->full_bw_cnt = 0;
bbr->cycle_mstamp.v64 = 0;
bbr->cycle_idx = 0;
bbr_reset_lt_bw_sampling(sk);
bbr_reset_startup_mode(sk);
}
static u32 bbr_sndbuf_expand(struct sock *sk)
{
/* Provision 3 * cwnd since BBR may slow-start even during recovery. */
return 3;
}
/* In theory BBR does not need to undo the cwnd since it does not
* always reduce cwnd on losses (see bbr_main()). Keep it for now.
*/
static u32 bbr_undo_cwnd(struct sock *sk)
{
return tcp_sk(sk)->snd_cwnd;
}
/* Entering loss recovery, so save cwnd for when we exit or undo recovery. */
static u32 bbr_ssthresh(struct sock *sk)
{
bbr_save_cwnd(sk);
return TCP_INFINITE_SSTHRESH; /* BBR does not use ssthresh */
}
static size_t bbr_get_info(struct sock *sk, u32 ext, int *attr,
union tcp_cc_info *info)
{
if (ext & (1 << (INET_DIAG_BBRINFO - 1)) ||
ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
u64 bw = bbr_bw(sk);
bw = bw * tp->mss_cache * USEC_PER_SEC >> BW_SCALE;
memset(&info->bbr, 0, sizeof(info->bbr));
info->bbr.bbr_bw_lo = (u32)bw;
info->bbr.bbr_bw_hi = (u32)(bw >> 32);
info->bbr.bbr_min_rtt = bbr->min_rtt_us;
info->bbr.bbr_pacing_gain = bbr->pacing_gain;
info->bbr.bbr_cwnd_gain = bbr->cwnd_gain;
*attr = INET_DIAG_BBRINFO;
return sizeof(info->bbr);
}
return 0;
}
static void bbr_set_state(struct sock *sk, u8 new_state)
{
struct bbr *bbr = inet_csk_ca(sk);
if (new_state == TCP_CA_Loss) {
struct rate_sample rs = { .losses = 1 };
bbr->prev_ca_state = TCP_CA_Loss;
bbr->full_bw = 0;
bbr->round_start = 1; /* treat RTO like end of a round */
bbr_lt_bw_sampling(sk, &rs);
}
}
static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = {
.flags = TCP_CONG_NON_RESTRICTED,
.name = "bbr",
.owner = THIS_MODULE,
.init = bbr_init,
.cong_control = bbr_main,
.sndbuf_expand = bbr_sndbuf_expand,
.undo_cwnd = bbr_undo_cwnd,
.cwnd_event = bbr_cwnd_event,
.ssthresh = bbr_ssthresh,
.tso_segs_goal = bbr_tso_segs_goal,
.get_info = bbr_get_info,
.set_state = bbr_set_state,
};
static int __init bbr_register(void)
{
BUILD_BUG_ON(sizeof(struct bbr) > ICSK_CA_PRIV_SIZE);
return tcp_register_congestion_control(&tcp_bbr_cong_ops);
}
static void __exit bbr_unregister(void)
{
tcp_unregister_congestion_control(&tcp_bbr_cong_ops);
}
module_init(bbr_register);
module_exit(bbr_unregister);
MODULE_AUTHOR("Van Jacobson <vanj@google.com>");
MODULE_AUTHOR("Neal Cardwell <ncardwell@google.com>");
MODULE_AUTHOR("Yuchung Cheng <ycheng@google.com>");
MODULE_AUTHOR("Soheil Hassas Yeganeh <soheil@google.com>");
MODULE_LICENSE("Dual BSD/GPL");
MODULE_DESCRIPTION("TCP BBR (Bottleneck Bandwidth and RTT)");

12
net/ipv4/tcp_cdg.c
View File

@ -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:

2
net/ipv4/tcp_cong.c
View File

@ -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;
}

152
net/ipv4/tcp_input.c
View File

@ -289,6 +289,7 @@ static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr
static void tcp_sndbuf_expand(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
int sndmem, per_mss;
u32 nr_segs;
@ -309,7 +310,8 @@ static void tcp_sndbuf_expand(struct sock *sk)
* Cubic needs 1.7 factor, rounded to 2 to include
* extra cushion (application might react slowly to POLLOUT)
*/
sndmem = 2 * nr_segs * per_mss;
sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
sndmem *= nr_segs * per_mss;
if (sk->sk_sndbuf < sndmem)
sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
@ -899,12 +901,29 @@ static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
}
/* Sum the number of packets on the wire we have marked as lost.
* There are two cases we care about here:
* a) Packet hasn't been marked lost (nor retransmitted),
* and this is the first loss.
* b) Packet has been marked both lost and retransmitted,
* and this means we think it was lost again.
*/
static void tcp_sum_lost(struct tcp_sock *tp, struct sk_buff *skb)
{
__u8 sacked = TCP_SKB_CB(skb)->sacked;
if (!(sacked & TCPCB_LOST) ||
((sacked & TCPCB_LOST) && (sacked & TCPCB_SACKED_RETRANS)))
tp->lost += tcp_skb_pcount(skb);
}
static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
{
if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
tcp_verify_retransmit_hint(tp, skb);
tp->lost_out += tcp_skb_pcount(skb);
tcp_sum_lost(tp, skb);
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
}
}
@ -913,6 +932,7 @@ void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
{
tcp_verify_retransmit_hint(tp, skb);
tcp_sum_lost(tp, skb);
if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
tp->lost_out += tcp_skb_pcount(skb);
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
@ -1094,6 +1114,7 @@ struct tcp_sacktag_state {
*/
struct skb_mstamp first_sackt;
struct skb_mstamp last_sackt;
struct rate_sample *rate;
int flag;
};
@ -1261,6 +1282,7 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
start_seq, end_seq, dup_sack, pcount,
&skb->skb_mstamp);
tcp_rate_skb_delivered(sk, skb, state->rate);
if (skb == tp->lost_skb_hint)
tp->lost_cnt_hint += pcount;
@ -1311,6 +1333,9 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
tcp_advance_highest_sack(sk, skb);
tcp_skb_collapse_tstamp(prev, skb);
if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp.v64))
TCP_SKB_CB(prev)->tx.delivered_mstamp.v64 = 0;
tcp_unlink_write_queue(skb, sk);
sk_wmem_free_skb(sk, skb);
@ -1540,6 +1565,7 @@ static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
dup_sack,
tcp_skb_pcount(skb),
&skb->skb_mstamp);
tcp_rate_skb_delivered(sk, skb, state->rate);
if (!before(TCP_SKB_CB(skb)->seq,
tcp_highest_sack_seq(tp)))
@ -1622,8 +1648,10 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
num_sacks, prior_snd_una);
if (found_dup_sack)
if (found_dup_sack) {
state->flag |= FLAG_DSACKING_ACK;
tp->delivered++; /* A spurious retransmission is delivered */
}
/* Eliminate too old ACKs, but take into
* account more or less fresh ones, they can
@ -1890,6 +1918,7 @@ void tcp_enter_loss(struct sock *sk)
struct sk_buff *skb;
bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
bool is_reneg; /* is receiver reneging on SACKs? */
bool mark_lost;
/* Reduce ssthresh if it has not yet been made inside this window. */
if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
@ -1923,8 +1952,12 @@ void tcp_enter_loss(struct sock *sk)
if (skb == tcp_send_head(sk))
break;
mark_lost = (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
is_reneg);
if (mark_lost)
tcp_sum_lost(tp, skb);
TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || is_reneg) {
if (mark_lost) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
tp->lost_out += tcp_skb_pcount(skb);
@ -2503,6 +2536,9 @@ static inline void tcp_end_cwnd_reduction(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
if (inet_csk(sk)->icsk_ca_ops->cong_control)
return;
/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
(tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
@ -2879,67 +2915,13 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
*rexmit = REXMIT_LOST;
}
/* Kathleen Nichols' algorithm for tracking the minimum 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.
*/
static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us)
{
const u32 now = tcp_time_stamp, wlen = sysctl_tcp_min_rtt_wlen * HZ;
struct rtt_meas *m = tcp_sk(sk)->rtt_min;
struct rtt_meas rttm = {
.rtt = likely(rtt_us) ? rtt_us : jiffies_to_usecs(1),
.ts = now,
};
u32 elapsed;
struct tcp_sock *tp = tcp_sk(sk);
u32 wlen = sysctl_tcp_min_rtt_wlen * HZ;
/* Check if the new measurement updates the 1st, 2nd, or 3rd choices */
if (unlikely(rttm.rtt <= m[0].rtt))
m[0] = m[1] = m[2] = rttm;
else if (rttm.rtt <= m[1].rtt)
m[1] = m[2] = rttm;
else if (rttm.rtt <= m[2].rtt)
m[2] = rttm;
elapsed = now - m[0].ts;
if (unlikely(elapsed > wlen)) {
/* Passed entire window without a new min so make 2nd choice
* the new min & 3rd choice the new 2nd. So forth and so on.
*/
m[0] = m[1];
m[1] = m[2];
m[2] = rttm;
if (now - m[0].ts > wlen) {
m[0] = m[1];
m[1] = rttm;
if (now - m[0].ts > wlen)
m[0] = rttm;
}
} else if (m[1].ts == m[0].ts && elapsed > wlen / 4) {
/* Passed a quarter of the window without a new min so
* take 2nd choice from the 2nd quarter of the window.
*/
m[2] = m[1] = rttm;
} else if (m[2].ts == m[1].ts && elapsed > wlen / 2) {
/* Passed half the window without a new min so take the 3rd
* choice from the last half of the window.
*/
m[2] = rttm;
}
minmax_running_min(&tp->rtt_min, wlen, tcp_time_stamp,
rtt_us ? : jiffies_to_usecs(1));
}
static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
@ -3102,10 +3084,11 @@ static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
*/
static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
u32 prior_snd_una, int *acked,
struct tcp_sacktag_state *sack)
struct tcp_sacktag_state *sack,
struct skb_mstamp *now)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct skb_mstamp first_ackt, last_ackt, now;
struct skb_mstamp first_ackt, last_ackt;
struct tcp_sock *tp = tcp_sk(sk);
u32 prior_sacked = tp->sacked_out;
u32 reord = tp->packets_out;
@ -3137,7 +3120,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
acked_pcount = tcp_tso_acked(sk, skb);
if (!acked_pcount)
break;
fully_acked = false;
} else {
/* Speedup tcp_unlink_write_queue() and next loop */
@ -3173,6 +3155,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
tp->packets_out -= acked_pcount;
pkts_acked += acked_pcount;
tcp_rate_skb_delivered(sk, skb, sack->rate);
/* Initial outgoing SYN's get put onto the write_queue
* just like anything else we transmit. It is not
@ -3205,16 +3188,15 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
flag |= FLAG_SACK_RENEGING;
skb_mstamp_get(&now);
if (likely(first_ackt.v64) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
seq_rtt_us = skb_mstamp_us_delta(&now, &first_ackt);
ca_rtt_us = skb_mstamp_us_delta(&now, &last_ackt);
seq_rtt_us = skb_mstamp_us_delta(now, &first_ackt);
ca_rtt_us = skb_mstamp_us_delta(now, &last_ackt);
}
if (sack->first_sackt.v64) {
sack_rtt_us = skb_mstamp_us_delta(&now, &sack->first_sackt);
ca_rtt_us = skb_mstamp_us_delta(&now, &sack->last_sackt);
sack_rtt_us = skb_mstamp_us_delta(now, &sack->first_sackt);
ca_rtt_us = skb_mstamp_us_delta(now, &sack->last_sackt);
}
sack->rate->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet, or -1 */
rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
ca_rtt_us);
@ -3242,7 +3224,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
tp->fackets_out -= min(pkts_acked, tp->fackets_out);
} else if (skb && rtt_update && sack_rtt_us >= 0 &&
sack_rtt_us > skb_mstamp_us_delta(&now, &skb->skb_mstamp)) {
sack_rtt_us > skb_mstamp_us_delta(now, &skb->skb_mstamp)) {
/* Do not re-arm RTO if the sack RTT is measured from data sent
* after when the head was last (re)transmitted. Otherwise the
* timeout may continue to extend in loss recovery.
@ -3333,8 +3315,15 @@ static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
* information. All transmission or retransmission are delayed afterwards.
*/
static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
int flag)
int flag, const struct rate_sample *rs)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
if (icsk->icsk_ca_ops->cong_control) {
icsk->icsk_ca_ops->cong_control(sk, rs);
return;
}
if (tcp_in_cwnd_reduction(sk)) {
/* Reduce cwnd if state mandates */
tcp_cwnd_reduction(sk, acked_sacked, flag);
@ -3579,17 +3568,21 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct tcp_sacktag_state sack_state;
struct rate_sample rs = { .prior_delivered = 0 };
u32 prior_snd_una = tp->snd_una;
u32 ack_seq = TCP_SKB_CB(skb)->seq;
u32 ack = TCP_SKB_CB(skb)->ack_seq;
bool is_dupack = false;
u32 prior_fackets;
int prior_packets = tp->packets_out;
u32 prior_delivered = tp->delivered;
u32 delivered = tp->delivered;
u32 lost = tp->lost;
int acked = 0; /* Number of packets newly acked */
int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
struct skb_mstamp now;
sack_state.first_sackt.v64 = 0;
sack_state.rate = &rs;
/* We very likely will need to access write queue head. */
prefetchw(sk->sk_write_queue.next);
@ -3612,6 +3605,8 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
if (after(ack, tp->snd_nxt))
goto invalid_ack;
skb_mstamp_get(&now);
if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
tcp_rearm_rto(sk);
@ -3622,6 +3617,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
}
prior_fackets = tp->fackets_out;
rs.prior_in_flight = tcp_packets_in_flight(tp);
/* ts_recent update must be made after we are sure that the packet
* is in window.
@ -3677,7 +3673,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
/* See if we can take anything off of the retransmit queue. */
flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una, &acked,
&sack_state);
&sack_state, &now);
if (tcp_ack_is_dubious(sk, flag)) {
is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
@ -3694,7 +3690,10 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
if (icsk->icsk_pending == ICSK_TIME_RETRANS)
tcp_schedule_loss_probe(sk);
tcp_cong_control(sk, ack, tp->delivered - prior_delivered, flag);
delivered = tp->delivered - delivered; /* freshly ACKed or SACKed */
lost = tp->lost - lost; /* freshly marked lost */
tcp_rate_gen(sk, delivered, lost, &now, &rs);
tcp_cong_control(sk, ack, delivered, flag, &rs);
tcp_xmit_recovery(sk, rexmit);
return 1;
@ -5993,7 +5992,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
} else
tcp_init_metrics(sk);
tcp_update_pacing_rate(sk);
if (!inet_csk(sk)->icsk_ca_ops->cong_control)
tcp_update_pacing_rate(sk);
/* Prevent spurious tcp_cwnd_restart() on first data packet */
tp->lsndtime = tcp_time_stamp;

5
net/ipv4/tcp_minisocks.c
View File

@ -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;

27
net/ipv4/tcp_output.c
View File

@ -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;

186
net/ipv4/tcp_rate.c Normal file
View File

@ -0,0 +1,186 @@
#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;
}

22
net/sched/sch_fq.c
View File

@ -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 @@ begin:
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 @@ begin:
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;