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308 lines
8.3 KiB
308 lines
8.3 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* TCP Westwood+: end-to-end bandwidth estimation for TCP |
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* |
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* Angelo Dell'Aera: author of the first version of TCP Westwood+ in Linux 2.4 |
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* |
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* Support at http://c3lab.poliba.it/index.php/Westwood |
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* Main references in literature: |
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* |
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* - Mascolo S, Casetti, M. Gerla et al. |
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* "TCP Westwood: bandwidth estimation for TCP" Proc. ACM Mobicom 2001 |
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* |
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* - A. Grieco, s. Mascolo |
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* "Performance evaluation of New Reno, Vegas, Westwood+ TCP" ACM Computer |
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* Comm. Review, 2004 |
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* |
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* - A. Dell'Aera, L. Grieco, S. Mascolo. |
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* "Linux 2.4 Implementation of Westwood+ TCP with Rate-Halving : |
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* A Performance Evaluation Over the Internet" (ICC 2004), Paris, June 2004 |
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* |
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* Westwood+ employs end-to-end bandwidth measurement to set cwnd and |
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* ssthresh after packet loss. The probing phase is as the original Reno. |
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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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/* TCP Westwood structure */ |
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struct westwood { |
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u32 bw_ns_est; /* first bandwidth estimation..not too smoothed 8) */ |
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u32 bw_est; /* bandwidth estimate */ |
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u32 rtt_win_sx; /* here starts a new evaluation... */ |
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u32 bk; |
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u32 snd_una; /* used for evaluating the number of acked bytes */ |
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u32 cumul_ack; |
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u32 accounted; |
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u32 rtt; |
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u32 rtt_min; /* minimum observed RTT */ |
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u8 first_ack; /* flag which infers that this is the first ack */ |
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u8 reset_rtt_min; /* Reset RTT min to next RTT sample*/ |
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}; |
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/* TCP Westwood functions and constants */ |
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#define TCP_WESTWOOD_RTT_MIN (HZ/20) /* 50ms */ |
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#define TCP_WESTWOOD_INIT_RTT (20*HZ) /* maybe too conservative?! */ |
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/* |
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* @tcp_westwood_create |
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* This function initializes fields used in TCP Westwood+, |
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* it is called after the initial SYN, so the sequence numbers |
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* are correct but new passive connections we have no |
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* information about RTTmin at this time so we simply set it to |
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* TCP_WESTWOOD_INIT_RTT. This value was chosen to be too conservative |
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* since in this way we're sure it will be updated in a consistent |
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* way as soon as possible. It will reasonably happen within the first |
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* RTT period of the connection lifetime. |
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*/ |
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static void tcp_westwood_init(struct sock *sk) |
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{ |
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struct westwood *w = inet_csk_ca(sk); |
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w->bk = 0; |
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w->bw_ns_est = 0; |
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w->bw_est = 0; |
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w->accounted = 0; |
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w->cumul_ack = 0; |
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w->reset_rtt_min = 1; |
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w->rtt_min = w->rtt = TCP_WESTWOOD_INIT_RTT; |
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w->rtt_win_sx = tcp_jiffies32; |
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w->snd_una = tcp_sk(sk)->snd_una; |
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w->first_ack = 1; |
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} |
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/* |
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* @westwood_do_filter |
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* Low-pass filter. Implemented using constant coefficients. |
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*/ |
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static inline u32 westwood_do_filter(u32 a, u32 b) |
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{ |
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return ((7 * a) + b) >> 3; |
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} |
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static void westwood_filter(struct westwood *w, u32 delta) |
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{ |
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/* If the filter is empty fill it with the first sample of bandwidth */ |
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if (w->bw_ns_est == 0 && w->bw_est == 0) { |
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w->bw_ns_est = w->bk / delta; |
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w->bw_est = w->bw_ns_est; |
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} else { |
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w->bw_ns_est = westwood_do_filter(w->bw_ns_est, w->bk / delta); |
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w->bw_est = westwood_do_filter(w->bw_est, w->bw_ns_est); |
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} |
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} |
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/* |
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* @westwood_pkts_acked |
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* Called after processing group of packets. |
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* but all westwood needs is the last sample of srtt. |
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*/ |
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static void tcp_westwood_pkts_acked(struct sock *sk, |
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const struct ack_sample *sample) |
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{ |
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struct westwood *w = inet_csk_ca(sk); |
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if (sample->rtt_us > 0) |
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w->rtt = usecs_to_jiffies(sample->rtt_us); |
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} |
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/* |
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* @westwood_update_window |
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* It updates RTT evaluation window if it is the right moment to do |
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* it. If so it calls filter for evaluating bandwidth. |
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*/ |
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static void westwood_update_window(struct sock *sk) |
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{ |
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struct westwood *w = inet_csk_ca(sk); |
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s32 delta = tcp_jiffies32 - w->rtt_win_sx; |
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/* Initialize w->snd_una with the first acked sequence number in order |
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* to fix mismatch between tp->snd_una and w->snd_una for the first |
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* bandwidth sample |
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*/ |
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if (w->first_ack) { |
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w->snd_una = tcp_sk(sk)->snd_una; |
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w->first_ack = 0; |
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} |
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/* |
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* See if a RTT-window has passed. |
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* Be careful since if RTT is less than |
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* 50ms we don't filter but we continue 'building the sample'. |
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* This minimum limit was chosen since an estimation on small |
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* time intervals is better to avoid... |
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* Obviously on a LAN we reasonably will always have |
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* right_bound = left_bound + WESTWOOD_RTT_MIN |
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*/ |
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if (w->rtt && delta > max_t(u32, w->rtt, TCP_WESTWOOD_RTT_MIN)) { |
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westwood_filter(w, delta); |
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w->bk = 0; |
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w->rtt_win_sx = tcp_jiffies32; |
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} |
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} |
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static inline void update_rtt_min(struct westwood *w) |
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{ |
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if (w->reset_rtt_min) { |
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w->rtt_min = w->rtt; |
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w->reset_rtt_min = 0; |
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} else |
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w->rtt_min = min(w->rtt, w->rtt_min); |
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} |
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/* |
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* @westwood_fast_bw |
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* It is called when we are in fast path. In particular it is called when |
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* header prediction is successful. In such case in fact update is |
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* straight forward and doesn't need any particular care. |
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*/ |
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static inline void westwood_fast_bw(struct sock *sk) |
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{ |
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const struct tcp_sock *tp = tcp_sk(sk); |
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struct westwood *w = inet_csk_ca(sk); |
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westwood_update_window(sk); |
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w->bk += tp->snd_una - w->snd_una; |
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w->snd_una = tp->snd_una; |
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update_rtt_min(w); |
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} |
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/* |
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* @westwood_acked_count |
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* This function evaluates cumul_ack for evaluating bk in case of |
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* delayed or partial acks. |
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*/ |
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static inline u32 westwood_acked_count(struct sock *sk) |
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{ |
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const struct tcp_sock *tp = tcp_sk(sk); |
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struct westwood *w = inet_csk_ca(sk); |
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w->cumul_ack = tp->snd_una - w->snd_una; |
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/* If cumul_ack is 0 this is a dupack since it's not moving |
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* tp->snd_una. |
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*/ |
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if (!w->cumul_ack) { |
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w->accounted += tp->mss_cache; |
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w->cumul_ack = tp->mss_cache; |
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} |
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if (w->cumul_ack > tp->mss_cache) { |
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/* Partial or delayed ack */ |
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if (w->accounted >= w->cumul_ack) { |
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w->accounted -= w->cumul_ack; |
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w->cumul_ack = tp->mss_cache; |
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} else { |
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w->cumul_ack -= w->accounted; |
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w->accounted = 0; |
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} |
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} |
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w->snd_una = tp->snd_una; |
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return w->cumul_ack; |
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} |
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/* |
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* TCP Westwood |
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* Here limit is evaluated as Bw estimation*RTTmin (for obtaining it |
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* in packets we use mss_cache). Rttmin is guaranteed to be >= 2 |
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* so avoids ever returning 0. |
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*/ |
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static u32 tcp_westwood_bw_rttmin(const struct sock *sk) |
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{ |
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const struct tcp_sock *tp = tcp_sk(sk); |
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const struct westwood *w = inet_csk_ca(sk); |
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return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2); |
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} |
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static void tcp_westwood_ack(struct sock *sk, u32 ack_flags) |
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{ |
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if (ack_flags & CA_ACK_SLOWPATH) { |
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struct westwood *w = inet_csk_ca(sk); |
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westwood_update_window(sk); |
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w->bk += westwood_acked_count(sk); |
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update_rtt_min(w); |
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return; |
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} |
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westwood_fast_bw(sk); |
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} |
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static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event) |
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{ |
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struct tcp_sock *tp = tcp_sk(sk); |
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struct westwood *w = inet_csk_ca(sk); |
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switch (event) { |
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case CA_EVENT_COMPLETE_CWR: |
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tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk); |
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break; |
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case CA_EVENT_LOSS: |
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tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk); |
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/* Update RTT_min when next ack arrives */ |
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w->reset_rtt_min = 1; |
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break; |
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default: |
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/* don't care */ |
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break; |
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} |
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} |
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/* Extract info for Tcp socket info provided via netlink. */ |
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static size_t tcp_westwood_info(struct sock *sk, u32 ext, int *attr, |
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union tcp_cc_info *info) |
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{ |
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const struct westwood *ca = inet_csk_ca(sk); |
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if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) { |
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info->vegas.tcpv_enabled = 1; |
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info->vegas.tcpv_rttcnt = 0; |
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info->vegas.tcpv_rtt = jiffies_to_usecs(ca->rtt); |
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info->vegas.tcpv_minrtt = jiffies_to_usecs(ca->rtt_min); |
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*attr = INET_DIAG_VEGASINFO; |
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return sizeof(struct tcpvegas_info); |
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} |
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return 0; |
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} |
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static struct tcp_congestion_ops tcp_westwood __read_mostly = { |
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.init = tcp_westwood_init, |
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.ssthresh = tcp_reno_ssthresh, |
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.cong_avoid = tcp_reno_cong_avoid, |
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.undo_cwnd = tcp_reno_undo_cwnd, |
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.cwnd_event = tcp_westwood_event, |
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.in_ack_event = tcp_westwood_ack, |
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.get_info = tcp_westwood_info, |
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.pkts_acked = tcp_westwood_pkts_acked, |
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.owner = THIS_MODULE, |
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.name = "westwood" |
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}; |
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static int __init tcp_westwood_register(void) |
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{ |
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BUILD_BUG_ON(sizeof(struct westwood) > ICSK_CA_PRIV_SIZE); |
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return tcp_register_congestion_control(&tcp_westwood); |
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} |
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static void __exit tcp_westwood_unregister(void) |
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{ |
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tcp_unregister_congestion_control(&tcp_westwood); |
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} |
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module_init(tcp_westwood_register); |
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module_exit(tcp_westwood_unregister); |
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MODULE_AUTHOR("Stephen Hemminger, Angelo Dell'Aera"); |
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MODULE_LICENSE("GPL"); |
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MODULE_DESCRIPTION("TCP Westwood+");
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