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tcp: add NV congestion control

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TCP-NV (New Vegas) is a major update to TCP-Vegas.
An earlier version of NV was presented at 2010's LPC.
It is a delayed based congestion avoidance for the
data center. This version has been tested within a
10G rack where the HW RTTs are 20-50us and with
1 to 400 flows.

A description of TCP-NV, including implementation
details as well as experimental results, can be found at:
http://www.brakmo.org/networking/tcp-nv/TCPNV.html

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Lawrence Brakmo 2016-06-08 21:16:45 -07:00 committed by David S. Miller
parent 6f094b9ec6
commit 699fafafab
3 changed files with 493 additions and 0 deletions
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16
net/ipv4/Kconfig
View File

@ -532,6 +532,22 @@ config TCP_CONG_VEGAS
window. TCP Vegas should provide less packet loss, but it is
not as aggressive as TCP Reno.
config TCP_CONG_NV
tristate "TCP NV"
default n
---help---
TCP NV is a follow up to TCP Vegas. It has been modified to deal with
10G networks, measurement noise introduced by LRO, GRO and interrupt
coalescence. In addition, it will decrease its cwnd multiplicatively
instead of linearly.
Note that in general congestion avoidance (cwnd decreased when # packets
queued grows) cannot coexist with congestion control (cwnd decreased only
when there is packet loss) due to fairness issues. One scenario when they
can coexist safely is when the CA flows have RTTs << CC flows RTTs.
For further details see http://www.brakmo.org/networking/tcp-nv/
config TCP_CONG_SCALABLE
tristate "Scalable TCP"
default n

1
net/ipv4/Makefile
View File

@ -50,6 +50,7 @@ obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_highspeed.o
obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o
obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.o
obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o
obj-$(CONFIG_TCP_CONG_NV) += tcp_nv.o
obj-$(CONFIG_TCP_CONG_VENO) += tcp_veno.o
obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o
obj-$(CONFIG_TCP_CONG_LP) += tcp_lp.o

476
net/ipv4/tcp_nv.c Normal file
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@ -0,0 +1,476 @@
/*
* TCP NV: TCP with Congestion Avoidance
*
* TCP-NV is a successor of TCP-Vegas that has been developed to
* deal with the issues that occur in modern networks.
* Like TCP-Vegas, TCP-NV supports true congestion avoidance,
* the ability to detect congestion before packet losses occur.
* When congestion (queue buildup) starts to occur, TCP-NV
* predicts what the cwnd size should be for the current
* throughput and it reduces the cwnd proportionally to
* the difference between the current cwnd and the predicted cwnd.
*
* NV is only recommeneded for traffic within a data center, and when
* all the flows are NV (at least those within the data center). This
* is due to the inherent unfairness between flows using losses to
* detect congestion (congestion control) and those that use queue
* buildup to detect congestion (congestion avoidance).
*
* Note: High NIC coalescence values may lower the performance of NV
* due to the increased noise in RTT values. In particular, we have
* seen issues with rx-frames values greater than 8.
*
* TODO:
* 1) Add mechanism to deal with reverse congestion.
*/
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/math64.h>
#include <net/tcp.h>
#include <linux/inet_diag.h>
/* TCP NV parameters
*
* nv_pad Max number of queued packets allowed in network
* nv_pad_buffer Do not grow cwnd if this closed to nv_pad
* nv_reset_period How often (in) seconds)to reset min_rtt
* nv_min_cwnd Don't decrease cwnd below this if there are no losses
* nv_cong_dec_mult Decrease cwnd by X% (30%) of congestion when detected
* nv_ssthresh_factor On congestion set ssthresh to this * <desired cwnd> / 8
* nv_rtt_factor RTT averaging factor
* nv_loss_dec_factor Decrease cwnd by this (50%) when losses occur
* nv_dec_eval_min_calls Wait this many RTT measurements before dec cwnd
* nv_inc_eval_min_calls Wait this many RTT measurements before inc cwnd
* nv_ssthresh_eval_min_calls Wait this many RTT measurements before stopping
* slow-start due to congestion
* nv_stop_rtt_cnt Only grow cwnd for this many RTTs after non-congestion
* nv_rtt_min_cnt Wait these many RTTs before making congesion decision
* nv_cwnd_growth_rate_neg
* nv_cwnd_growth_rate_pos
* How quickly to double growth rate (not rate) of cwnd when not
* congested. One value (nv_cwnd_growth_rate_neg) for when
* rate < 1 pkt/RTT (after losses). The other (nv_cwnd_growth_rate_pos)
* otherwise.
*/
static int nv_pad __read_mostly = 10;
static int nv_pad_buffer __read_mostly = 2;
static int nv_reset_period __read_mostly = 5; /* in seconds */
static int nv_min_cwnd __read_mostly = 2;
static int nv_cong_dec_mult __read_mostly = 30 * 128 / 100; /* = 30% */
static int nv_ssthresh_factor __read_mostly = 8; /* = 1 */
static int nv_rtt_factor __read_mostly = 128; /* = 1/2*old + 1/2*new */
static int nv_loss_dec_factor __read_mostly = 512; /* => 50% */
static int nv_cwnd_growth_rate_neg __read_mostly = 8;
static int nv_cwnd_growth_rate_pos __read_mostly; /* 0 => fixed like Reno */
static int nv_dec_eval_min_calls __read_mostly = 60;
static int nv_inc_eval_min_calls __read_mostly = 20;
static int nv_ssthresh_eval_min_calls __read_mostly = 30;
static int nv_stop_rtt_cnt __read_mostly = 10;
static int nv_rtt_min_cnt __read_mostly = 2;
module_param(nv_pad, int, 0644);
MODULE_PARM_DESC(nv_pad, "max queued packets allowed in network");
module_param(nv_reset_period, int, 0644);
MODULE_PARM_DESC(nv_reset_period, "nv_min_rtt reset period (secs)");
module_param(nv_min_cwnd, int, 0644);
MODULE_PARM_DESC(nv_min_cwnd, "NV will not decrease cwnd below this value"
" without losses");
/* TCP NV Parameters */
struct tcpnv {
unsigned long nv_min_rtt_reset_jiffies; /* when to switch to
* nv_min_rtt_new */
s8 cwnd_growth_factor; /* Current cwnd growth factor,
* < 0 => less than 1 packet/RTT */
u8 available8;
u16 available16;
u32 loss_cwnd; /* cwnd at last loss */
u8 nv_allow_cwnd_growth:1, /* whether cwnd can grow */
nv_reset:1, /* whether to reset values */
nv_catchup:1; /* whether we are growing because
* of temporary cwnd decrease */
u8 nv_eval_call_cnt; /* call count since last eval */
u8 nv_min_cwnd; /* nv won't make a ca decision if cwnd is
* smaller than this. It may grow to handle
* TSO, LRO and interrupt coalescence because
* with these a small cwnd cannot saturate
* the link. Note that this is different from
* the file local nv_min_cwnd */
u8 nv_rtt_cnt; /* RTTs without making ca decision */;
u32 nv_last_rtt; /* last rtt */
u32 nv_min_rtt; /* active min rtt. Used to determine slope */
u32 nv_min_rtt_new; /* min rtt for future use */
u32 nv_rtt_max_rate; /* max rate seen during current RTT */
u32 nv_rtt_start_seq; /* current RTT ends when packet arrives
* acking beyond nv_rtt_start_seq */
u32 nv_last_snd_una; /* Previous value of tp->snd_una. It is
* used to determine bytes acked since last
* call to bictcp_acked */
u32 nv_no_cong_cnt; /* Consecutive no congestion decisions */
};
#define NV_INIT_RTT U32_MAX
#define NV_MIN_CWND 4
#define NV_MIN_CWND_GROW 2
#define NV_TSO_CWND_BOUND 80
static inline void tcpnv_reset(struct tcpnv *ca, struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
ca->nv_reset = 0;
ca->loss_cwnd = 0;
ca->nv_no_cong_cnt = 0;
ca->nv_rtt_cnt = 0;
ca->nv_last_rtt = 0;
ca->nv_rtt_max_rate = 0;
ca->nv_rtt_start_seq = tp->snd_una;
ca->nv_eval_call_cnt = 0;
ca->nv_last_snd_una = tp->snd_una;
}
static void tcpnv_init(struct sock *sk)
{
struct tcpnv *ca = inet_csk_ca(sk);
tcpnv_reset(ca, sk);
ca->nv_allow_cwnd_growth = 1;
ca->nv_min_rtt_reset_jiffies = jiffies + 2 * HZ;
ca->nv_min_rtt = NV_INIT_RTT;
ca->nv_min_rtt_new = NV_INIT_RTT;
ca->nv_min_cwnd = NV_MIN_CWND;
ca->nv_catchup = 0;
ca->cwnd_growth_factor = 0;
}
static void tcpnv_cong_avoid(struct sock *sk, u32 ack, u32 acked)
{
struct tcp_sock *tp = tcp_sk(sk);
struct tcpnv *ca = inet_csk_ca(sk);
u32 cnt;
if (!tcp_is_cwnd_limited(sk))
return;
/* Only grow cwnd if NV has not detected congestion */
if (!ca->nv_allow_cwnd_growth)
return;
if (tcp_in_slow_start(tp)) {
acked = tcp_slow_start(tp, acked);
if (!acked)
return;
}
if (ca->cwnd_growth_factor < 0) {
cnt = tp->snd_cwnd << -ca->cwnd_growth_factor;
tcp_cong_avoid_ai(tp, cnt, acked);
} else {
cnt = max(4U, tp->snd_cwnd >> ca->cwnd_growth_factor);
tcp_cong_avoid_ai(tp, cnt, acked);
}
}
static u32 tcpnv_recalc_ssthresh(struct sock *sk)
{
const struct tcp_sock *tp = tcp_sk(sk);
struct tcpnv *ca = inet_csk_ca(sk);
ca->loss_cwnd = tp->snd_cwnd;
return max((tp->snd_cwnd * nv_loss_dec_factor) >> 10, 2U);
}
static u32 tcpnv_undo_cwnd(struct sock *sk)
{
struct tcpnv *ca = inet_csk_ca(sk);
return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
}
static void tcpnv_state(struct sock *sk, u8 new_state)
{
struct tcpnv *ca = inet_csk_ca(sk);
if (new_state == TCP_CA_Open && ca->nv_reset) {
tcpnv_reset(ca, sk);
} else if (new_state == TCP_CA_Loss || new_state == TCP_CA_CWR ||
new_state == TCP_CA_Recovery) {
ca->nv_reset = 1;
ca->nv_allow_cwnd_growth = 0;
if (new_state == TCP_CA_Loss) {
/* Reset cwnd growth factor to Reno value */
if (ca->cwnd_growth_factor > 0)
ca->cwnd_growth_factor = 0;
/* Decrease growth rate if allowed */
if (nv_cwnd_growth_rate_neg > 0 &&
ca->cwnd_growth_factor > -8)
ca->cwnd_growth_factor--;
}
}
}
/* Do congestion avoidance calculations for TCP-NV
*/
static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample)
{
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct tcpnv *ca = inet_csk_ca(sk);
unsigned long now = jiffies;
s64 rate64 = 0;
u32 rate, max_win, cwnd_by_slope;
u32 avg_rtt;
u32 bytes_acked = 0;
/* Some calls are for duplicates without timetamps */
if (sample->rtt_us < 0)
return;
/* If not in TCP_CA_Open or TCP_CA_Disorder states, skip. */
if (icsk->icsk_ca_state != TCP_CA_Open &&
icsk->icsk_ca_state != TCP_CA_Disorder)
return;
/* Stop cwnd growth if we were in catch up mode */
if (ca->nv_catchup && tp->snd_cwnd >= nv_min_cwnd) {
ca->nv_catchup = 0;
ca->nv_allow_cwnd_growth = 0;
}
bytes_acked = tp->snd_una - ca->nv_last_snd_una;
ca->nv_last_snd_una = tp->snd_una;
if (sample->in_flight == 0)
return;
/* Calculate moving average of RTT */
if (nv_rtt_factor > 0) {
if (ca->nv_last_rtt > 0) {
avg_rtt = (((u64)sample->rtt_us) * nv_rtt_factor +
((u64)ca->nv_last_rtt)
* (256 - nv_rtt_factor)) >> 8;
} else {
avg_rtt = sample->rtt_us;
ca->nv_min_rtt = avg_rtt << 1;
}
ca->nv_last_rtt = avg_rtt;
} else {
avg_rtt = sample->rtt_us;
}
/* rate in 100's bits per second */
rate64 = ((u64)sample->in_flight) * 8000000;
rate = (u32)div64_u64(rate64, (u64)(avg_rtt * 100));
/* Remember the maximum rate seen during this RTT
* Note: It may be more than one RTT. This function should be
* called at least nv_dec_eval_min_calls times.
*/
if (ca->nv_rtt_max_rate < rate)
ca->nv_rtt_max_rate = rate;
/* We have valid information, increment counter */
if (ca->nv_eval_call_cnt < 255)
ca->nv_eval_call_cnt++;
/* update min rtt if necessary */
if (avg_rtt < ca->nv_min_rtt)
ca->nv_min_rtt = avg_rtt;
/* update future min_rtt if necessary */
if (avg_rtt < ca->nv_min_rtt_new)
ca->nv_min_rtt_new = avg_rtt;
/* nv_min_rtt is updated with the minimum (possibley averaged) rtt
* seen in the last sysctl_tcp_nv_reset_period seconds (i.e. a
* warm reset). This new nv_min_rtt will be continued to be updated
* and be used for another sysctl_tcp_nv_reset_period seconds,
* when it will be updated again.
* In practice we introduce some randomness, so the actual period used
* is chosen randomly from the range:
* [sysctl_tcp_nv_reset_period*3/4, sysctl_tcp_nv_reset_period*5/4)
*/
if (time_after_eq(now, ca->nv_min_rtt_reset_jiffies)) {
unsigned char rand;
ca->nv_min_rtt = ca->nv_min_rtt_new;
ca->nv_min_rtt_new = NV_INIT_RTT;
get_random_bytes(&rand, 1);
ca->nv_min_rtt_reset_jiffies =
now + ((nv_reset_period * (384 + rand) * HZ) >> 9);
/* Every so often we decrease ca->nv_min_cwnd in case previous
* value is no longer accurate.
*/
ca->nv_min_cwnd = max(ca->nv_min_cwnd / 2, NV_MIN_CWND);
}
/* Once per RTT check if we need to do congestion avoidance */
if (before(ca->nv_rtt_start_seq, tp->snd_una)) {
ca->nv_rtt_start_seq = tp->snd_nxt;
if (ca->nv_rtt_cnt < 0xff)
/* Increase counter for RTTs without CA decision */
ca->nv_rtt_cnt++;
/* If this function is only called once within an RTT
* the cwnd is probably too small (in some cases due to
* tso, lro or interrupt coalescence), so we increase
* ca->nv_min_cwnd.
*/
if (ca->nv_eval_call_cnt == 1 &&
bytes_acked >= (ca->nv_min_cwnd - 1) * tp->mss_cache &&
ca->nv_min_cwnd < (NV_TSO_CWND_BOUND + 1)) {
ca->nv_min_cwnd = min(ca->nv_min_cwnd
+ NV_MIN_CWND_GROW,
NV_TSO_CWND_BOUND + 1);
ca->nv_rtt_start_seq = tp->snd_nxt +
ca->nv_min_cwnd * tp->mss_cache;
ca->nv_eval_call_cnt = 0;
ca->nv_allow_cwnd_growth = 1;
return;
}
/* Find the ideal cwnd for current rate from slope
* slope = 80000.0 * mss / nv_min_rtt
* cwnd_by_slope = nv_rtt_max_rate / slope
*/
cwnd_by_slope = (u32)
div64_u64(((u64)ca->nv_rtt_max_rate) * ca->nv_min_rtt,
(u64)(80000 * tp->mss_cache));
max_win = cwnd_by_slope + nv_pad;
/* If cwnd > max_win, decrease cwnd
* if cwnd < max_win, grow cwnd
* else leave the same
*/
if (tp->snd_cwnd > max_win) {
/* there is congestion, check that it is ok
* to make a CA decision
* 1. We should have at least nv_dec_eval_min_calls
* data points before making a CA decision
* 2. We only make a congesion decision after
* nv_rtt_min_cnt RTTs
*/
if (ca->nv_rtt_cnt < nv_rtt_min_cnt) {
return;
} else if (tp->snd_ssthresh == TCP_INFINITE_SSTHRESH) {
if (ca->nv_eval_call_cnt <
nv_ssthresh_eval_min_calls)
return;
/* otherwise we will decrease cwnd */
} else if (ca->nv_eval_call_cnt <
nv_dec_eval_min_calls) {
if (ca->nv_allow_cwnd_growth &&
ca->nv_rtt_cnt > nv_stop_rtt_cnt)
ca->nv_allow_cwnd_growth = 0;
return;
}
/* We have enough data to determine we are congested */
ca->nv_allow_cwnd_growth = 0;
tp->snd_ssthresh =
(nv_ssthresh_factor * max_win) >> 3;
if (tp->snd_cwnd - max_win > 2) {
/* gap > 2, we do exponential cwnd decrease */
int dec;
dec = max(2U, ((tp->snd_cwnd - max_win) *
nv_cong_dec_mult) >> 7);
tp->snd_cwnd -= dec;
} else if (nv_cong_dec_mult > 0) {
tp->snd_cwnd = max_win;
}
if (ca->cwnd_growth_factor > 0)
ca->cwnd_growth_factor = 0;
ca->nv_no_cong_cnt = 0;
} else if (tp->snd_cwnd <= max_win - nv_pad_buffer) {
/* There is no congestion, grow cwnd if allowed*/
if (ca->nv_eval_call_cnt < nv_inc_eval_min_calls)
return;
ca->nv_allow_cwnd_growth = 1;
ca->nv_no_cong_cnt++;
if (ca->cwnd_growth_factor < 0 &&
nv_cwnd_growth_rate_neg > 0 &&
ca->nv_no_cong_cnt > nv_cwnd_growth_rate_neg) {
ca->cwnd_growth_factor++;
ca->nv_no_cong_cnt = 0;
} else if (ca->cwnd_growth_factor >= 0 &&
nv_cwnd_growth_rate_pos > 0 &&
ca->nv_no_cong_cnt >
nv_cwnd_growth_rate_pos) {
ca->cwnd_growth_factor++;
ca->nv_no_cong_cnt = 0;
}
} else {
/* cwnd is in-between, so do nothing */
return;
}
/* update state */
ca->nv_eval_call_cnt = 0;
ca->nv_rtt_cnt = 0;
ca->nv_rtt_max_rate = 0;
/* Don't want to make cwnd < nv_min_cwnd
* (it wasn't before, if it is now is because nv
* decreased it).
*/
if (tp->snd_cwnd < nv_min_cwnd)
tp->snd_cwnd = nv_min_cwnd;
}
}
/* Extract info for Tcp socket info provided via netlink */
size_t tcpnv_get_info(struct sock *sk, u32 ext, int *attr,
union tcp_cc_info *info)
{
const struct tcpnv *ca = inet_csk_ca(sk);
if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
info->vegas.tcpv_enabled = 1;
info->vegas.tcpv_rttcnt = ca->nv_rtt_cnt;
info->vegas.tcpv_rtt = ca->nv_last_rtt;
info->vegas.tcpv_minrtt = ca->nv_min_rtt;
*attr = INET_DIAG_VEGASINFO;
return sizeof(struct tcpvegas_info);
}
return 0;
}
EXPORT_SYMBOL_GPL(tcpnv_get_info);
static struct tcp_congestion_ops tcpnv __read_mostly = {
.init = tcpnv_init,
.ssthresh = tcpnv_recalc_ssthresh,
.cong_avoid = tcpnv_cong_avoid,
.set_state = tcpnv_state,
.undo_cwnd = tcpnv_undo_cwnd,
.pkts_acked = tcpnv_acked,
.get_info = tcpnv_get_info,
.owner = THIS_MODULE,
.name = "nv",
};
static int __init tcpnv_register(void)
{
BUILD_BUG_ON(sizeof(struct tcpnv) > ICSK_CA_PRIV_SIZE);
return tcp_register_congestion_control(&tcpnv);
}
static void __exit tcpnv_unregister(void)
{
tcp_unregister_congestion_control(&tcpnv);
}
module_init(tcpnv_register);
module_exit(tcpnv_unregister);
MODULE_AUTHOR("Lawrence Brakmo");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("TCP NV");
MODULE_VERSION("1.0");