Hi all,
It's definately better to do rtt measurements in the proper callback
like you're suggesting since the call to cong_avoid depends on too many
factors (ECN, FRTO) that shouldn't inhibit rtt sampling though they,
for a period, determine how cwnd must be set...
--
i.
On Thu, 19 Jul 2007, Stephen Hemminger wrote:
> Remove use of received timestamp option value from RTT calculation in Cubic.
> A hostile receiver may be returning a larger timestamp option than the
> original
> value. This would cause the sender to believe the malevolent receiver had
> a larger RTT and because Cubic tries to provide some RTT friendliness, the
> sender would then favor the liar.
>
> Instead, use the jiffie resolutionRTT value already computed and
> passed back after ack.
>
> Signed-off-by: Stephen Hemminger <[EMAIL PROTECTED]>
>
> --- a/net/ipv4/tcp_cubic.c 2007-07-19 08:21:42.000000000 +0100
> +++ b/net/ipv4/tcp_cubic.c 2007-07-19 08:24:58.000000000 +0100
> @@ -246,38 +246,12 @@ static inline void bictcp_update(struct
> ca->cnt = 1;
> }
>
> -
> -/* Keep track of minimum rtt */
> -static inline void measure_delay(struct sock *sk)
> -{
> - const struct tcp_sock *tp = tcp_sk(sk);
> - struct bictcp *ca = inet_csk_ca(sk);
> - u32 delay;
> -
> - /* No time stamp */
> - if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) ||
> - /* Discard delay samples right after fast recovery */
> - (s32)(tcp_time_stamp - ca->epoch_start) < HZ)
> - return;
> -
> - delay = (tcp_time_stamp - tp->rx_opt.rcv_tsecr)<<3;
> - if (delay == 0)
> - delay = 1;
> -
> - /* first time call or link delay decreases */
> - if (ca->delay_min == 0 || ca->delay_min > delay)
> - ca->delay_min = delay;
> -}
> -
> static void bictcp_cong_avoid(struct sock *sk, u32 ack,
> u32 seq_rtt, u32 in_flight, int data_acked)
> {
> struct tcp_sock *tp = tcp_sk(sk);
> struct bictcp *ca = inet_csk_ca(sk);
>
> - if (data_acked)
> - measure_delay(sk);
> -
> if (!tcp_is_cwnd_limited(sk, in_flight))
> return;
>
> @@ -337,14 +311,30 @@ static void bictcp_state(struct sock *sk
> static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
> {
> const struct inet_connection_sock *icsk = inet_csk(sk);
> + struct bictcp *ca = inet_csk_ca(sk);
> + u32 delay;
>
> if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) {
> - struct bictcp *ca = inet_csk_ca(sk);
> cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
> ca->delayed_ack += cnt;
> }
> -}
>
> + /* Some calls are for duplicates without timetamps */
> + if (rtt_us < 0)
> + return;
> +
> + /* Discard delay samples right after fast recovery */
> + if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)
> + return;
> +
> + delay = usecs_to_jiffies(rtt_us) << 3;
> + if (delay == 0)
> + delay = 1;
> +
> + /* first time call or link delay decreases */
> + if (ca->delay_min == 0 || ca->delay_min > delay)
> + ca->delay_min = delay;
> +}
>
> static struct tcp_congestion_ops cubictcp = {
> .init = bictcp_init,
>
>
-
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