Re: [PATCH net-next] tcp: Make SYN ACK RTO tunable by BPF programs with TFO

[Neal Cardwell <ncardwell@google.com>]

On Mon, Aug 15, 2022 at 8:30 PM Jie Meng <jmeng@fb.com> wrote:
>
> Instead of the hardcoded TCP_TIMEOUT_INIT, this diff calls tcp_timeout_init
> to initiate req->timeout like the non TFO SYN ACK case.
>
> Tested using the following packetdrill script, on a host with a BPF
> program that sets the initial connect timeout to 10ms.
>
> `../../common/defaults.sh`
>
> // Initialize connection
>     0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
>    +0 setsockopt(3, SOL_TCP, TCP_FASTOPEN, [1], 4) = 0
>    +0 bind(3, ..., ...) = 0
>    +0 listen(3, 1) = 0
>
>    +0 < S 0:0(0) win 32792 <mss 1000,sackOK,FO TFO_COOKIE>
>    +0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
>    +.01 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
>    +.02 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
>    +.04 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
>    +.01 < . 1:1(0) ack 1 win 32792
>
>    +0 accept(3, ..., ...) = 4
>
> Signed-off-by: Jie Meng <jmeng@fb.com>
> ---
>  net/ipv4/tcp_fastopen.c | 3 ++-
>  net/ipv4/tcp_timer.c    | 2 +-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
> index 825b216d11f5..45cc7f1ca296 100644
> --- a/net/ipv4/tcp_fastopen.c
> +++ b/net/ipv4/tcp_fastopen.c
> @@ -272,8 +272,9 @@ static struct sock *tcp_fastopen_create_child(struct sock *sk,
>          * The request socket is not added to the ehash
>          * because it's been added to the accept queue directly.
>          */
> +       req->timeout = tcp_timeout_init(child);
>         inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,
> -                                 TCP_TIMEOUT_INIT, TCP_RTO_MAX);
> +                                 req->timeout, TCP_RTO_MAX);
>
>         refcount_set(&req->rsk_refcnt, 2);
>
> diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> index b4dfb82d6ecb..cb79127f45c3 100644
> --- a/net/ipv4/tcp_timer.c
> +++ b/net/ipv4/tcp_timer.c
> @@ -428,7 +428,7 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
>         if (!tp->retrans_stamp)
>                 tp->retrans_stamp = tcp_time_stamp(tp);
>         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
> -                         TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
> +                         req->timeout << req->num_timeout, TCP_RTO_MAX);
>  }
>
>
> --

Looks good to me. Thanks for the feature!

Acked-by: Neal Cardwell <ncardwell@google.com>

neal