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https://github.com/torvalds/linux
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e73ebb0881
LRO, GRO, delayed ACKs, and middleboxes can cause "stretch ACKs" that cover more than the RFC-specified maximum of 2 packets. These stretch ACKs can cause serious performance shortfalls in common congestion control algorithms that were designed and tuned years ago with receiver hosts that were not using LRO or GRO, and were instead politely ACKing every other packet. This patch series fixes Reno and CUBIC to handle stretch ACKs. This patch prepares for the upcoming stretch ACK bug fix patches. It adds an "acked" parameter to tcp_cong_avoid_ai() to allow for future fixes to tcp_cong_avoid_ai() to correctly handle stretch ACKs, and changes all congestion control algorithms to pass in 1 for the ACKed count. It also changes tcp_slow_start() to return the number of packet ACK "credits" that were not processed in slow start mode, and can be processed by the congestion control module in additive increase mode. In future patches we will fix tcp_cong_avoid_ai() to handle stretch ACKs, and fix Reno and CUBIC handling of stretch ACKs in slow start and additive increase mode. Reported-by: Eyal Perry <eyalpe@mellanox.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
62 lines
1.4 KiB
C
62 lines
1.4 KiB
C
/* Tom Kelly's Scalable TCP
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*
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* See http://www.deneholme.net/tom/scalable/
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*
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* John Heffner <jheffner@sc.edu>
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*/
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#include <linux/module.h>
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#include <net/tcp.h>
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/* These factors derived from the recommended values in the aer:
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* .01 and and 7/8. We use 50 instead of 100 to account for
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* delayed ack.
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*/
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#define TCP_SCALABLE_AI_CNT 50U
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#define TCP_SCALABLE_MD_SCALE 3
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static void tcp_scalable_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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if (!tcp_is_cwnd_limited(sk))
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return;
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if (tp->snd_cwnd <= tp->snd_ssthresh)
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tcp_slow_start(tp, acked);
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else
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tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT),
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1);
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}
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static u32 tcp_scalable_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 - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
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}
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static struct tcp_congestion_ops tcp_scalable __read_mostly = {
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.ssthresh = tcp_scalable_ssthresh,
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.cong_avoid = tcp_scalable_cong_avoid,
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.owner = THIS_MODULE,
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.name = "scalable",
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};
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static int __init tcp_scalable_register(void)
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{
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return tcp_register_congestion_control(&tcp_scalable);
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}
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static void __exit tcp_scalable_unregister(void)
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{
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tcp_unregister_congestion_control(&tcp_scalable);
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}
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module_init(tcp_scalable_register);
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module_exit(tcp_scalable_unregister);
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MODULE_AUTHOR("John Heffner");
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("Scalable TCP");
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