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239 lines
6.6 KiB
239 lines
6.6 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* |
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* YeAH TCP |
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* |
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* For further details look at: |
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* https://web.archive.org/web/20080316215752/http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf |
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* |
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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/skbuff.h> |
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#include <linux/inet_diag.h> |
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#include <net/tcp.h> |
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#include "tcp_vegas.h" |
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#define TCP_YEAH_ALPHA 80 /* number of packets queued at the bottleneck */ |
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#define TCP_YEAH_GAMMA 1 /* fraction of queue to be removed per rtt */ |
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#define TCP_YEAH_DELTA 3 /* log minimum fraction of cwnd to be removed on loss */ |
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#define TCP_YEAH_EPSILON 1 /* log maximum fraction to be removed on early decongestion */ |
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#define TCP_YEAH_PHY 8 /* maximum delta from base */ |
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#define TCP_YEAH_RHO 16 /* minimum number of consecutive rtt to consider competition on loss */ |
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#define TCP_YEAH_ZETA 50 /* minimum number of state switches to reset reno_count */ |
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#define TCP_SCALABLE_AI_CNT 100U |
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/* YeAH variables */ |
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struct yeah { |
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struct vegas vegas; /* must be first */ |
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/* YeAH */ |
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u32 lastQ; |
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u32 doing_reno_now; |
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u32 reno_count; |
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u32 fast_count; |
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}; |
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static void tcp_yeah_init(struct sock *sk) |
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{ |
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struct tcp_sock *tp = tcp_sk(sk); |
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struct yeah *yeah = inet_csk_ca(sk); |
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tcp_vegas_init(sk); |
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yeah->doing_reno_now = 0; |
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yeah->lastQ = 0; |
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yeah->reno_count = 2; |
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/* Ensure the MD arithmetic works. This is somewhat pedantic, |
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* since I don't think we will see a cwnd this large. :) */ |
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tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128); |
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} |
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static void tcp_yeah_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 yeah *yeah = inet_csk_ca(sk); |
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if (!tcp_is_cwnd_limited(sk)) |
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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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goto do_vegas; |
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} |
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if (!yeah->doing_reno_now) { |
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/* Scalable */ |
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tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT), |
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acked); |
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} else { |
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/* Reno */ |
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tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked); |
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} |
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/* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt. |
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* |
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* These are so named because they represent the approximate values |
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* of snd_una and snd_nxt at the beginning of the current RTT. More |
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* precisely, they represent the amount of data sent during the RTT. |
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* At the end of the RTT, when we receive an ACK for v_beg_snd_nxt, |
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* we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding |
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* bytes of data have been ACKed during the course of the RTT, giving |
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* an "actual" rate of: |
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* |
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* (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration) |
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* |
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* Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una, |
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* because delayed ACKs can cover more than one segment, so they |
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* don't line up yeahly with the boundaries of RTTs. |
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* |
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* Another unfortunate fact of life is that delayed ACKs delay the |
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* advance of the left edge of our send window, so that the number |
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* of bytes we send in an RTT is often less than our cwnd will allow. |
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* So we keep track of our cwnd separately, in v_beg_snd_cwnd. |
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*/ |
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do_vegas: |
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if (after(ack, yeah->vegas.beg_snd_nxt)) { |
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/* We do the Vegas calculations only if we got enough RTT |
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* samples that we can be reasonably sure that we got |
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* at least one RTT sample that wasn't from a delayed ACK. |
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* If we only had 2 samples total, |
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* then that means we're getting only 1 ACK per RTT, which |
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* means they're almost certainly delayed ACKs. |
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* If we have 3 samples, we should be OK. |
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*/ |
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if (yeah->vegas.cntRTT > 2) { |
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u32 rtt, queue; |
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u64 bw; |
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/* We have enough RTT samples, so, using the Vegas |
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* algorithm, we determine if we should increase or |
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* decrease cwnd, and by how much. |
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*/ |
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/* Pluck out the RTT we are using for the Vegas |
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* calculations. This is the min RTT seen during the |
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* last RTT. Taking the min filters out the effects |
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* of delayed ACKs, at the cost of noticing congestion |
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* a bit later. |
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*/ |
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rtt = yeah->vegas.minRTT; |
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/* Compute excess number of packets above bandwidth |
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* Avoid doing full 64 bit divide. |
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*/ |
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bw = tp->snd_cwnd; |
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bw *= rtt - yeah->vegas.baseRTT; |
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do_div(bw, rtt); |
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queue = bw; |
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if (queue > TCP_YEAH_ALPHA || |
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rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) { |
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if (queue > TCP_YEAH_ALPHA && |
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tp->snd_cwnd > yeah->reno_count) { |
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u32 reduction = min(queue / TCP_YEAH_GAMMA , |
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tp->snd_cwnd >> TCP_YEAH_EPSILON); |
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tp->snd_cwnd -= reduction; |
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tp->snd_cwnd = max(tp->snd_cwnd, |
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yeah->reno_count); |
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tp->snd_ssthresh = tp->snd_cwnd; |
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} |
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if (yeah->reno_count <= 2) |
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yeah->reno_count = max(tp->snd_cwnd>>1, 2U); |
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else |
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yeah->reno_count++; |
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yeah->doing_reno_now = min(yeah->doing_reno_now + 1, |
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0xffffffU); |
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} else { |
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yeah->fast_count++; |
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if (yeah->fast_count > TCP_YEAH_ZETA) { |
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yeah->reno_count = 2; |
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yeah->fast_count = 0; |
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} |
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yeah->doing_reno_now = 0; |
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} |
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yeah->lastQ = queue; |
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} |
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/* Save the extent of the current window so we can use this |
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* at the end of the next RTT. |
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*/ |
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yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt; |
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yeah->vegas.beg_snd_nxt = tp->snd_nxt; |
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yeah->vegas.beg_snd_cwnd = tp->snd_cwnd; |
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/* Wipe the slate clean for the next RTT. */ |
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yeah->vegas.cntRTT = 0; |
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yeah->vegas.minRTT = 0x7fffffff; |
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} |
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} |
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static u32 tcp_yeah_ssthresh(struct sock *sk) |
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{ |
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const struct tcp_sock *tp = tcp_sk(sk); |
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struct yeah *yeah = inet_csk_ca(sk); |
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u32 reduction; |
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if (yeah->doing_reno_now < TCP_YEAH_RHO) { |
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reduction = yeah->lastQ; |
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reduction = min(reduction, max(tp->snd_cwnd>>1, 2U)); |
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reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA); |
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} else |
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reduction = max(tp->snd_cwnd>>1, 2U); |
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yeah->fast_count = 0; |
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yeah->reno_count = max(yeah->reno_count>>1, 2U); |
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return max_t(int, tp->snd_cwnd - reduction, 2); |
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} |
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static struct tcp_congestion_ops tcp_yeah __read_mostly = { |
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.init = tcp_yeah_init, |
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.ssthresh = tcp_yeah_ssthresh, |
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.undo_cwnd = tcp_reno_undo_cwnd, |
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.cong_avoid = tcp_yeah_cong_avoid, |
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.set_state = tcp_vegas_state, |
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.cwnd_event = tcp_vegas_cwnd_event, |
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.get_info = tcp_vegas_get_info, |
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.pkts_acked = tcp_vegas_pkts_acked, |
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.owner = THIS_MODULE, |
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.name = "yeah", |
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}; |
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static int __init tcp_yeah_register(void) |
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{ |
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BUILD_BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE); |
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tcp_register_congestion_control(&tcp_yeah); |
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return 0; |
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} |
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static void __exit tcp_yeah_unregister(void) |
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{ |
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tcp_unregister_congestion_control(&tcp_yeah); |
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} |
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module_init(tcp_yeah_register); |
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module_exit(tcp_yeah_unregister); |
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MODULE_AUTHOR("Angelo P. Castellani"); |
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MODULE_LICENSE("GPL"); |
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MODULE_DESCRIPTION("YeAH TCP");
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