503 lines
16 KiB
C
503 lines
16 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* TCP NV: TCP with Congestion Avoidance
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*
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* TCP-NV is a successor of TCP-Vegas that has been developed to
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* deal with the issues that occur in modern networks.
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* Like TCP-Vegas, TCP-NV supports true congestion avoidance,
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* the ability to detect congestion before packet losses occur.
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* When congestion (queue buildup) starts to occur, TCP-NV
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* predicts what the cwnd size should be for the current
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* throughput and it reduces the cwnd proportionally to
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* the difference between the current cwnd and the predicted cwnd.
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*
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* NV is only recommeneded for traffic within a data center, and when
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* all the flows are NV (at least those within the data center). This
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* is due to the inherent unfairness between flows using losses to
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* detect congestion (congestion control) and those that use queue
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* buildup to detect congestion (congestion avoidance).
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*
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* Note: High NIC coalescence values may lower the performance of NV
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* due to the increased noise in RTT values. In particular, we have
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* seen issues with rx-frames values greater than 8.
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*
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* TODO:
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* 1) Add mechanism to deal with reverse congestion.
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*/
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#include <linux/mm.h>
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#include <linux/module.h>
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#include <linux/math64.h>
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#include <net/tcp.h>
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#include <linux/inet_diag.h>
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/* TCP NV parameters
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*
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* nv_pad Max number of queued packets allowed in network
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* nv_pad_buffer Do not grow cwnd if this closed to nv_pad
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* nv_reset_period How often (in) seconds)to reset min_rtt
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* nv_min_cwnd Don't decrease cwnd below this if there are no losses
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* nv_cong_dec_mult Decrease cwnd by X% (30%) of congestion when detected
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* nv_ssthresh_factor On congestion set ssthresh to this * <desired cwnd> / 8
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* nv_rtt_factor RTT averaging factor
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* nv_loss_dec_factor Decrease cwnd to this (80%) when losses occur
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* nv_dec_eval_min_calls Wait this many RTT measurements before dec cwnd
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* nv_inc_eval_min_calls Wait this many RTT measurements before inc cwnd
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* nv_ssthresh_eval_min_calls Wait this many RTT measurements before stopping
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* slow-start due to congestion
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* nv_stop_rtt_cnt Only grow cwnd for this many RTTs after non-congestion
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* nv_rtt_min_cnt Wait these many RTTs before making congesion decision
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* nv_cwnd_growth_rate_neg
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* nv_cwnd_growth_rate_pos
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* How quickly to double growth rate (not rate) of cwnd when not
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* congested. One value (nv_cwnd_growth_rate_neg) for when
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* rate < 1 pkt/RTT (after losses). The other (nv_cwnd_growth_rate_pos)
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* otherwise.
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*/
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static int nv_pad __read_mostly = 10;
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static int nv_pad_buffer __read_mostly = 2;
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static int nv_reset_period __read_mostly = 5; /* in seconds */
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static int nv_min_cwnd __read_mostly = 2;
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static int nv_cong_dec_mult __read_mostly = 30 * 128 / 100; /* = 30% */
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static int nv_ssthresh_factor __read_mostly = 8; /* = 1 */
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static int nv_rtt_factor __read_mostly = 128; /* = 1/2*old + 1/2*new */
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static int nv_loss_dec_factor __read_mostly = 819; /* => 80% */
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static int nv_cwnd_growth_rate_neg __read_mostly = 8;
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static int nv_cwnd_growth_rate_pos __read_mostly; /* 0 => fixed like Reno */
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static int nv_dec_eval_min_calls __read_mostly = 60;
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static int nv_inc_eval_min_calls __read_mostly = 20;
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static int nv_ssthresh_eval_min_calls __read_mostly = 30;
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static int nv_stop_rtt_cnt __read_mostly = 10;
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static int nv_rtt_min_cnt __read_mostly = 2;
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module_param(nv_pad, int, 0644);
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MODULE_PARM_DESC(nv_pad, "max queued packets allowed in network");
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module_param(nv_reset_period, int, 0644);
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MODULE_PARM_DESC(nv_reset_period, "nv_min_rtt reset period (secs)");
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module_param(nv_min_cwnd, int, 0644);
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MODULE_PARM_DESC(nv_min_cwnd, "NV will not decrease cwnd below this value"
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" without losses");
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/* TCP NV Parameters */
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struct tcpnv {
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unsigned long nv_min_rtt_reset_jiffies; /* when to switch to
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* nv_min_rtt_new */
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s8 cwnd_growth_factor; /* Current cwnd growth factor,
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* < 0 => less than 1 packet/RTT */
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u8 available8;
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u16 available16;
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u8 nv_allow_cwnd_growth:1, /* whether cwnd can grow */
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nv_reset:1, /* whether to reset values */
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nv_catchup:1; /* whether we are growing because
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* of temporary cwnd decrease */
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u8 nv_eval_call_cnt; /* call count since last eval */
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u8 nv_min_cwnd; /* nv won't make a ca decision if cwnd is
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* smaller than this. It may grow to handle
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* TSO, LRO and interrupt coalescence because
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* with these a small cwnd cannot saturate
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* the link. Note that this is different from
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* the file local nv_min_cwnd */
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u8 nv_rtt_cnt; /* RTTs without making ca decision */;
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u32 nv_last_rtt; /* last rtt */
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u32 nv_min_rtt; /* active min rtt. Used to determine slope */
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u32 nv_min_rtt_new; /* min rtt for future use */
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u32 nv_base_rtt; /* If non-zero it represents the threshold for
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* congestion */
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u32 nv_lower_bound_rtt; /* Used in conjunction with nv_base_rtt. It is
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* set to 80% of nv_base_rtt. It helps reduce
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* unfairness between flows */
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u32 nv_rtt_max_rate; /* max rate seen during current RTT */
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u32 nv_rtt_start_seq; /* current RTT ends when packet arrives
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* acking beyond nv_rtt_start_seq */
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u32 nv_last_snd_una; /* Previous value of tp->snd_una. It is
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* used to determine bytes acked since last
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* call to bictcp_acked */
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u32 nv_no_cong_cnt; /* Consecutive no congestion decisions */
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};
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#define NV_INIT_RTT U32_MAX
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#define NV_MIN_CWND 4
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#define NV_MIN_CWND_GROW 2
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#define NV_TSO_CWND_BOUND 80
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static inline void tcpnv_reset(struct tcpnv *ca, struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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ca->nv_reset = 0;
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ca->nv_no_cong_cnt = 0;
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ca->nv_rtt_cnt = 0;
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ca->nv_last_rtt = 0;
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ca->nv_rtt_max_rate = 0;
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ca->nv_rtt_start_seq = tp->snd_una;
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ca->nv_eval_call_cnt = 0;
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ca->nv_last_snd_una = tp->snd_una;
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}
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static void tcpnv_init(struct sock *sk)
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{
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struct tcpnv *ca = inet_csk_ca(sk);
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int base_rtt;
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tcpnv_reset(ca, sk);
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/* See if base_rtt is available from socket_ops bpf program.
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* It is meant to be used in environments, such as communication
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* within a datacenter, where we have reasonable estimates of
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* RTTs
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*/
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base_rtt = tcp_call_bpf(sk, BPF_SOCK_OPS_BASE_RTT, 0, NULL);
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if (base_rtt > 0) {
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ca->nv_base_rtt = base_rtt;
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ca->nv_lower_bound_rtt = (base_rtt * 205) >> 8; /* 80% */
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} else {
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ca->nv_base_rtt = 0;
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ca->nv_lower_bound_rtt = 0;
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}
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ca->nv_allow_cwnd_growth = 1;
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ca->nv_min_rtt_reset_jiffies = jiffies + 2 * HZ;
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ca->nv_min_rtt = NV_INIT_RTT;
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ca->nv_min_rtt_new = NV_INIT_RTT;
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ca->nv_min_cwnd = NV_MIN_CWND;
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ca->nv_catchup = 0;
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ca->cwnd_growth_factor = 0;
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}
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/* If provided, apply upper (base_rtt) and lower (lower_bound_rtt)
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* bounds to RTT.
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*/
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inline u32 nv_get_bounded_rtt(struct tcpnv *ca, u32 val)
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{
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if (ca->nv_lower_bound_rtt > 0 && val < ca->nv_lower_bound_rtt)
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return ca->nv_lower_bound_rtt;
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else if (ca->nv_base_rtt > 0 && val > ca->nv_base_rtt)
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return ca->nv_base_rtt;
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else
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return val;
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}
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static void tcpnv_cong_avoid(struct sock *sk, u32 ack, u32 acked)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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struct tcpnv *ca = inet_csk_ca(sk);
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u32 cnt;
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if (!tcp_is_cwnd_limited(sk))
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return;
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/* Only grow cwnd if NV has not detected congestion */
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if (!ca->nv_allow_cwnd_growth)
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return;
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if (tcp_in_slow_start(tp)) {
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acked = tcp_slow_start(tp, acked);
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if (!acked)
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return;
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}
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if (ca->cwnd_growth_factor < 0) {
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cnt = tp->snd_cwnd << -ca->cwnd_growth_factor;
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tcp_cong_avoid_ai(tp, cnt, acked);
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} else {
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cnt = max(4U, tp->snd_cwnd >> ca->cwnd_growth_factor);
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tcp_cong_avoid_ai(tp, cnt, acked);
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}
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}
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static u32 tcpnv_recalc_ssthresh(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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return max((tp->snd_cwnd * nv_loss_dec_factor) >> 10, 2U);
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}
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static void tcpnv_state(struct sock *sk, u8 new_state)
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{
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struct tcpnv *ca = inet_csk_ca(sk);
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if (new_state == TCP_CA_Open && ca->nv_reset) {
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tcpnv_reset(ca, sk);
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} else if (new_state == TCP_CA_Loss || new_state == TCP_CA_CWR ||
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new_state == TCP_CA_Recovery) {
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ca->nv_reset = 1;
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ca->nv_allow_cwnd_growth = 0;
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if (new_state == TCP_CA_Loss) {
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/* Reset cwnd growth factor to Reno value */
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if (ca->cwnd_growth_factor > 0)
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ca->cwnd_growth_factor = 0;
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/* Decrease growth rate if allowed */
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if (nv_cwnd_growth_rate_neg > 0 &&
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ca->cwnd_growth_factor > -8)
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ca->cwnd_growth_factor--;
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}
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}
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}
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/* Do congestion avoidance calculations for TCP-NV
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*/
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static void tcpnv_acked(struct sock *sk, const struct ack_sample *sample)
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{
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const struct inet_connection_sock *icsk = inet_csk(sk);
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struct tcp_sock *tp = tcp_sk(sk);
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struct tcpnv *ca = inet_csk_ca(sk);
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unsigned long now = jiffies;
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u64 rate64;
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u32 rate, max_win, cwnd_by_slope;
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u32 avg_rtt;
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u32 bytes_acked = 0;
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/* Some calls are for duplicates without timetamps */
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if (sample->rtt_us < 0)
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return;
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/* If not in TCP_CA_Open or TCP_CA_Disorder states, skip. */
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if (icsk->icsk_ca_state != TCP_CA_Open &&
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icsk->icsk_ca_state != TCP_CA_Disorder)
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return;
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/* Stop cwnd growth if we were in catch up mode */
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if (ca->nv_catchup && tp->snd_cwnd >= nv_min_cwnd) {
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ca->nv_catchup = 0;
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ca->nv_allow_cwnd_growth = 0;
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}
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bytes_acked = tp->snd_una - ca->nv_last_snd_una;
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ca->nv_last_snd_una = tp->snd_una;
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if (sample->in_flight == 0)
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return;
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/* Calculate moving average of RTT */
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if (nv_rtt_factor > 0) {
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if (ca->nv_last_rtt > 0) {
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avg_rtt = (((u64)sample->rtt_us) * nv_rtt_factor +
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((u64)ca->nv_last_rtt)
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* (256 - nv_rtt_factor)) >> 8;
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} else {
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avg_rtt = sample->rtt_us;
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ca->nv_min_rtt = avg_rtt << 1;
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}
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ca->nv_last_rtt = avg_rtt;
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} else {
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avg_rtt = sample->rtt_us;
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}
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/* rate in 100's bits per second */
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rate64 = ((u64)sample->in_flight) * 80000;
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do_div(rate64, avg_rtt ?: 1);
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rate = (u32)rate64;
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/* Remember the maximum rate seen during this RTT
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* Note: It may be more than one RTT. This function should be
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* called at least nv_dec_eval_min_calls times.
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*/
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if (ca->nv_rtt_max_rate < rate)
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ca->nv_rtt_max_rate = rate;
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/* We have valid information, increment counter */
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if (ca->nv_eval_call_cnt < 255)
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ca->nv_eval_call_cnt++;
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/* Apply bounds to rtt. Only used to update min_rtt */
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avg_rtt = nv_get_bounded_rtt(ca, avg_rtt);
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/* update min rtt if necessary */
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if (avg_rtt < ca->nv_min_rtt)
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ca->nv_min_rtt = avg_rtt;
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/* update future min_rtt if necessary */
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if (avg_rtt < ca->nv_min_rtt_new)
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ca->nv_min_rtt_new = avg_rtt;
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/* nv_min_rtt is updated with the minimum (possibley averaged) rtt
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* seen in the last sysctl_tcp_nv_reset_period seconds (i.e. a
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* warm reset). This new nv_min_rtt will be continued to be updated
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* and be used for another sysctl_tcp_nv_reset_period seconds,
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* when it will be updated again.
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* In practice we introduce some randomness, so the actual period used
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* is chosen randomly from the range:
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* [sysctl_tcp_nv_reset_period*3/4, sysctl_tcp_nv_reset_period*5/4)
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*/
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if (time_after_eq(now, ca->nv_min_rtt_reset_jiffies)) {
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unsigned char rand;
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ca->nv_min_rtt = ca->nv_min_rtt_new;
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ca->nv_min_rtt_new = NV_INIT_RTT;
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get_random_bytes(&rand, 1);
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ca->nv_min_rtt_reset_jiffies =
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now + ((nv_reset_period * (384 + rand) * HZ) >> 9);
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/* Every so often we decrease ca->nv_min_cwnd in case previous
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* value is no longer accurate.
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*/
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ca->nv_min_cwnd = max(ca->nv_min_cwnd / 2, NV_MIN_CWND);
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}
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/* Once per RTT check if we need to do congestion avoidance */
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if (before(ca->nv_rtt_start_seq, tp->snd_una)) {
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ca->nv_rtt_start_seq = tp->snd_nxt;
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if (ca->nv_rtt_cnt < 0xff)
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/* Increase counter for RTTs without CA decision */
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ca->nv_rtt_cnt++;
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/* If this function is only called once within an RTT
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* the cwnd is probably too small (in some cases due to
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* tso, lro or interrupt coalescence), so we increase
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* ca->nv_min_cwnd.
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*/
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if (ca->nv_eval_call_cnt == 1 &&
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bytes_acked >= (ca->nv_min_cwnd - 1) * tp->mss_cache &&
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ca->nv_min_cwnd < (NV_TSO_CWND_BOUND + 1)) {
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ca->nv_min_cwnd = min(ca->nv_min_cwnd
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+ NV_MIN_CWND_GROW,
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NV_TSO_CWND_BOUND + 1);
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ca->nv_rtt_start_seq = tp->snd_nxt +
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ca->nv_min_cwnd * tp->mss_cache;
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ca->nv_eval_call_cnt = 0;
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ca->nv_allow_cwnd_growth = 1;
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return;
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}
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/* Find the ideal cwnd for current rate from slope
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* slope = 80000.0 * mss / nv_min_rtt
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* cwnd_by_slope = nv_rtt_max_rate / slope
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*/
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cwnd_by_slope = (u32)
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div64_u64(((u64)ca->nv_rtt_max_rate) * ca->nv_min_rtt,
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80000ULL * tp->mss_cache);
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max_win = cwnd_by_slope + nv_pad;
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/* If cwnd > max_win, decrease cwnd
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* if cwnd < max_win, grow cwnd
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* else leave the same
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*/
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if (tp->snd_cwnd > max_win) {
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/* there is congestion, check that it is ok
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* to make a CA decision
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* 1. We should have at least nv_dec_eval_min_calls
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* data points before making a CA decision
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* 2. We only make a congesion decision after
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* nv_rtt_min_cnt RTTs
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*/
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if (ca->nv_rtt_cnt < nv_rtt_min_cnt) {
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return;
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} else if (tp->snd_ssthresh == TCP_INFINITE_SSTHRESH) {
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if (ca->nv_eval_call_cnt <
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nv_ssthresh_eval_min_calls)
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return;
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/* otherwise we will decrease cwnd */
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} else if (ca->nv_eval_call_cnt <
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nv_dec_eval_min_calls) {
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if (ca->nv_allow_cwnd_growth &&
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ca->nv_rtt_cnt > nv_stop_rtt_cnt)
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ca->nv_allow_cwnd_growth = 0;
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return;
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}
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/* We have enough data to determine we are congested */
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ca->nv_allow_cwnd_growth = 0;
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tp->snd_ssthresh =
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(nv_ssthresh_factor * max_win) >> 3;
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if (tp->snd_cwnd - max_win > 2) {
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/* gap > 2, we do exponential cwnd decrease */
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int dec;
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dec = max(2U, ((tp->snd_cwnd - max_win) *
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nv_cong_dec_mult) >> 7);
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tp->snd_cwnd -= dec;
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} else if (nv_cong_dec_mult > 0) {
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tp->snd_cwnd = max_win;
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}
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if (ca->cwnd_growth_factor > 0)
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ca->cwnd_growth_factor = 0;
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ca->nv_no_cong_cnt = 0;
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} else if (tp->snd_cwnd <= max_win - nv_pad_buffer) {
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/* There is no congestion, grow cwnd if allowed*/
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if (ca->nv_eval_call_cnt < nv_inc_eval_min_calls)
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return;
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ca->nv_allow_cwnd_growth = 1;
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ca->nv_no_cong_cnt++;
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if (ca->cwnd_growth_factor < 0 &&
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nv_cwnd_growth_rate_neg > 0 &&
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ca->nv_no_cong_cnt > nv_cwnd_growth_rate_neg) {
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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");
|