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-rw-r--r--net/ipv4/tcp_nv.c501
1 files changed, 501 insertions, 0 deletions
diff --git a/net/ipv4/tcp_nv.c b/net/ipv4/tcp_nv.c
new file mode 100644
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--- /dev/null
+++ b/net/ipv4/tcp_nv.c
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+/*
+ * 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, 0, NULL);
+ 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;
+ u64 rate64;
+ 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) * 80000;
+ do_div(rate64, avg_rtt ?: 1);
+ rate = (u32)rate64;
+
+ /* 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,
+ 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 */
+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");
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-24 10:54:42 +0000