/* * * YeAH TCP * * For further details look at: * https://web.archive.org/web/20080316215752/http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf * */ #include #include #include #include #include #include "tcp_vegas.h" #define TCP_YEAH_ALPHA 80 /* number of packets queued at the bottleneck */ #define TCP_YEAH_GAMMA 1 /* fraction of queue to be removed per rtt */ #define TCP_YEAH_DELTA 3 /* log minimum fraction of cwnd to be removed on loss */ #define TCP_YEAH_EPSILON 1 /* log maximum fraction to be removed on early decongestion */ #define TCP_YEAH_PHY 8 /* maximum delta from base */ #define TCP_YEAH_RHO 16 /* minimum number of consecutive rtt to consider competition on loss */ #define TCP_YEAH_ZETA 50 /* minimum number of state switches to reset reno_count */ #define TCP_SCALABLE_AI_CNT 100U /* YeAH variables */ struct yeah { struct vegas vegas; /* must be first */ /* YeAH */ u32 lastQ; u32 doing_reno_now; u32 reno_count; u32 fast_count; u32 pkts_acked; u32 loss_cwnd; }; static void tcp_yeah_init(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct yeah *yeah = inet_csk_ca(sk); tcp_vegas_init(sk); yeah->doing_reno_now = 0; yeah->lastQ = 0; yeah->reno_count = 2; /* Ensure the MD arithmetic works. This is somewhat pedantic, * since I don't think we will see a cwnd this large. :) */ tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128); } static void tcp_yeah_pkts_acked(struct sock *sk, const struct ack_sample *sample) { const struct inet_connection_sock *icsk = inet_csk(sk); struct yeah *yeah = inet_csk_ca(sk); if (icsk->icsk_ca_state == TCP_CA_Open) yeah->pkts_acked = sample->pkts_acked; tcp_vegas_pkts_acked(sk, sample); } static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 acked) { struct tcp_sock *tp = tcp_sk(sk); struct yeah *yeah = inet_csk_ca(sk); if (!tcp_is_cwnd_limited(sk)) return; if (tcp_in_slow_start(tp)) tcp_slow_start(tp, acked); else if (!yeah->doing_reno_now) { /* Scalable */ tp->snd_cwnd_cnt += yeah->pkts_acked; if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)) { if (tp->snd_cwnd < tp->snd_cwnd_clamp) tp->snd_cwnd++; tp->snd_cwnd_cnt = 0; } yeah->pkts_acked = 1; } else { /* Reno */ tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1); } /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt. * * These are so named because they represent the approximate values * of snd_una and snd_nxt at the beginning of the current RTT. More * precisely, they represent the amount of data sent during the RTT. * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt, * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding * bytes of data have been ACKed during the course of the RTT, giving * an "actual" rate of: * * (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration) * * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una, * because delayed ACKs can cover more than one segment, so they * don't line up yeahly with the boundaries of RTTs. * * Another unfortunate fact of life is that delayed ACKs delay the * advance of the left edge of our send window, so that the number * of bytes we send in an RTT is often less than our cwnd will allow. * So we keep track of our cwnd separately, in v_beg_snd_cwnd. */ if (after(ack, yeah->vegas.beg_snd_nxt)) { /* We do the Vegas calculations only if we got enough RTT * samples that we can be reasonably sure that we got * at least one RTT sample that wasn't from a delayed ACK. * If we only had 2 samples total, * then that means we're getting only 1 ACK per RTT, which * means they're almost certainly delayed ACKs. * If we have 3 samples, we should be OK. */ if (yeah->vegas.cntRTT > 2) { u32 rtt, queue; u64 bw; /* We have enough RTT samples, so, using the Vegas * algorithm, we determine if we should increase or * decrease cwnd, and by how much. */ /* Pluck out the RTT we are using for the Vegas * calculations. This is the min RTT seen during the * last RTT. Taking the min filters out the effects * of delayed ACKs, at the cost of noticing congestion * a bit later. */ rtt = yeah->vegas.minRTT; /* Compute excess number of packets above bandwidth * Avoid doing full 64 bit divide. */ bw = tp->snd_cwnd; bw *= rtt - yeah->vegas.baseRTT; do_div(bw, rtt); queue = bw; if (queue > TCP_YEAH_ALPHA || rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) { if (queue > TCP_YEAH_ALPHA && tp->snd_cwnd > yeah->reno_count) { u32 reduction = min(queue / TCP_YEAH_GAMMA , tp->snd_cwnd >> TCP_YEAH_EPSILON); tp->snd_cwnd -= reduction; tp->snd_cwnd = max(tp->snd_cwnd, yeah->reno_count); tp->snd_ssthresh = tp->snd_cwnd; } if (yeah->reno_count <= 2) yeah->reno_count = max(tp->snd_cwnd>>1, 2U); else yeah->reno_count++; yeah->doing_reno_now = min(yeah->doing_reno_now + 1, 0xffffffU); } else { yeah->fast_count++; if (yeah->fast_count > TCP_YEAH_ZETA) { yeah->reno_count = 2; yeah->fast_count = 0; } yeah->doing_reno_now = 0; } yeah->lastQ = queue; } /* Save the extent of the current window so we can use this * at the end of the next RTT. */ yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt; yeah->vegas.beg_snd_nxt = tp->snd_nxt; yeah->vegas.beg_snd_cwnd = tp->snd_cwnd; /* Wipe the slate clean for the next RTT. */ yeah->vegas.cntRTT = 0; yeah->vegas.minRTT = 0x7fffffff; } } static u32 tcp_yeah_ssthresh(struct sock *sk) { const struct tcp_sock *tp = tcp_sk(sk); struct yeah *yeah = inet_csk_ca(sk); u32 reduction; if (yeah->doing_reno_now < TCP_YEAH_RHO) { reduction = yeah->lastQ; reduction = min(reduction, max(tp->snd_cwnd>>1, 2U)); reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA); } else reduction = max(tp->snd_cwnd>>1, 2U); yeah->fast_count = 0; yeah->reno_count = max(yeah->reno_count>>1, 2U); yeah->loss_cwnd = tp->snd_cwnd; return max_t(int, tp->snd_cwnd - reduction, 2); } static u32 tcp_yeah_cwnd_undo(struct sock *sk) { const struct yeah *yeah = inet_csk_ca(sk); return max(tcp_sk(sk)->snd_cwnd, yeah->loss_cwnd); } static struct tcp_congestion_ops tcp_yeah __read_mostly = { .init = tcp_yeah_init, .ssthresh = tcp_yeah_ssthresh, .undo_cwnd = tcp_yeah_cwnd_undo, .cong_avoid = tcp_yeah_cong_avoid, .set_state = tcp_vegas_state, .cwnd_event = tcp_vegas_cwnd_event, .get_info = tcp_vegas_get_info, .pkts_acked = tcp_yeah_pkts_acked, .owner = THIS_MODULE, .name = "yeah", }; static int __init tcp_yeah_register(void) { BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE); tcp_register_congestion_control(&tcp_yeah); return 0; } static void __exit tcp_yeah_unregister(void) { tcp_unregister_congestion_control(&tcp_yeah); } module_init(tcp_yeah_register); module_exit(tcp_yeah_unregister); MODULE_AUTHOR("Angelo P. Castellani"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("YeAH TCP"); the kernel summit. - New documentation for the device_link mechanism. ... and, of course, lots of typo fixes and small updates" * tag 'docs-4.10' of git://git.lwn.net/linux: (193 commits) dma-buf: Extract dma-buf.rst Update Documentation/00-INDEX docs: 00-INDEX: document directories/files with no docs docs: 00-INDEX: remove non-existing entries docs: 00-INDEX: add missing entries for documentation files/dirs docs: 00-INDEX: consolidate process/ and admin-guide/ description scripts: add a script to check if Documentation/00-INDEX is sane Docs: change sh -> awk in REPORTING-BUGS Documentation/core-api/device_link: Add initial documentation core-api: remove an unexpected unident ppc/idle: Add documentation for powersave=off Doc: Correct typo, "Introdution" => "Introduction" Documentation/atomic_ops.txt: convert to ReST markup Documentation/local_ops.txt: convert to ReST markup Documentation/assoc_array.txt: convert to ReST markup docs-rst: parse-headers.pl: cleanup the documentation docs-rst: fix media cleandocs target docs-rst: media/Makefile: reorganize the rules docs-rst: media: build SVG from graphviz files docs-rst: replace bayer.png by a SVG image ...
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