Re: Get amount of fast retransmissions from TCP info

[Neal Cardwell]

On Wed, May 3, 2017 at 3:47 PM, Lars Erik StorbukÃs
<storbukas.dev@xxxxxxxxx> wrote:
> I also want to count the amount of ECN signals received. Do anyone
> have any input on where to place an ECN signal count?
>
> Is any of these locations a logical place to increase the ECN counter
> (which I've created in tcp_sock)? Both locations are in the
> tcp_input.c.
>
> /* In tcp_fastretrans_alert() */
> if (flag & FLAG_ECE) {
>     tp->prior_ssthresh = 0;
>     tp->ecn_count += 1; // ECN counter
> }

This approach sounds good to me.

> or
>
> /* In tcp_enter_recovery() */
> if (!tcp_in_cwnd_reduction(sk)) {
>     if (!ece_ack)
>         tp->prior_ssthresh = tcp_current_ssthresh(sk);
>     else
>        tp->ecn_count += 1; // ECN counter
>     tcp_init_cwnd_reduction(sk);
> }
> tcp_set_ca_state(sk, TCP_CA_Recovery);

This location would only count ECE marks we happened to get at the
moment we enter loss recovery.

neal