477 lines
15 KiB
C
477 lines
15 KiB
C
/*
|
|
* 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 ?: 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++;
|
|
|
|
/* 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,
|
|
80000ULL * 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");
|