/*
* 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 to this (80%) 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 = 819; /* => 80% */
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;
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_base_rtt; /* If non-zero it represents the threshold for
* congestion */
u32 nv_lower_bound_rtt; /* Used in conjunction with nv_base_rtt. It is
* set to 80% of nv_base_rtt. It helps reduce
* unfairness between flows */
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->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);
int base_rtt;
tcpnv_reset(ca, sk);
/* See if base_rtt is available from socket_ops bpf program.
* It is meant to be used in environments, such as communication
* within a datacenter, where we have reasonable estimates of
* RTTs
*/
base_rtt = tcp_call_bpf(sk, BPF_SOCK_OPS_BASE_RTT);
if (base_rtt > 0) {
ca->nv_base_rtt = base_rtt;
ca->nv_lower_bound_rtt = (base_rtt * 205) >> 8; /* 80% */
} else {
ca->nv_base_rtt = 0;
ca->nv_lower_bound_rtt = 0;
}
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;
}
/* If provided, apply upper (base_rtt) and lower (lower_bound_rtt)
* bounds to RTT.
*/
inline u32 nv_get_bounded_rtt(struct tcpnv *ca, u32 val)
{
if (ca->nv_lower_bound_rtt > 0 && val < ca->nv_lower_bound_rtt)
return ca->nv_lower_bound_rtt;
else if (ca->nv_base_rtt > 0 && val > ca->nv_base_rtt)
return ca->nv_base_rtt;
else
return val;
}
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);
return max((tp->snd_cwnd * nv_loss_dec_factor) >> 10, 2U);
}
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 ?: 1) * 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++;
/* Apply bounds to rtt. Only used to update min_rtt */
avg_rtt = nv_get_bounded_rtt(ca, avg_rtt);
/* 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 */
static 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;
}
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 = tcp_reno_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");
