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Message-ID: <CAF0XkCANsVVYBeaD8A=Y5NR_=SF=11Vto75HD+O45RGZD2tKYQ@mail.gmail.com> Date: Sat, 27 May 2017 14:12:22 +0200 From: Lars Erik Storbukås <storbukas.dev@...il.com> To: Netdev <netdev@...r.kernel.org> Subject: TCP get SND_CWND change on loss event I want to store the value of snd_cwnd when a congestion event occurs (value before snd_cwnd is reduced), and the new value of snd_cwnd (the value it has been reduced to). In other words: the congestion window before and after a congestion event occurs. I'm uncertain where (and how) it would be logical to implement this. I have found two possible locations in the tcp_input.c where (I think) it could be implemented: static void tcp_cong_control(...) { ... if (tcp_in_cwnd_reduction(sk)) { struct tcp_sock *tp = tcp_sk(sk); prior_congestion_window = tp->snd_cwnd; /* Reduce cwnd if state mandates */ tcp_cwnd_reduction(sk, acked_sacked, flag); reduced_congestion_window = tp->snd_cwnd; } ... } or static void tcp_fastretrans_alert(...) { ... default: ... struct tcp_sock *tp = tcp_sk(sk); prior_congestion_window = tp->snd_cwnd; /* Otherwise enter Recovery state */ tcp_enter_recovery(sk, (flag & FLAG_ECE)); fast_rexmit = 1; reduced_congestion_window = tp->snd_cwnd; ... } Does anyone have advice on where (and how) to implement this? Does any of the proposed solutions above seem logical? / Lars Erik Storbukås
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