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

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Date:   Tue, 16 Aug 2022 09:11:32 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     Jie Meng <jmeng@...com>, netdev@...r.kernel.org, kafai@...com,
        kuba@...nel.org, edumazet@...gle.com, bpf@...r.kernel.org,
        Wei Wang <weiwan@...gle.com>
Subject: Re: [PATCH net-next] tcp: Make SYN ACK RTO tunable by BPF programs
 with TFO

On Tue, Aug 16, 2022 at 6:37 AM Neal Cardwell <ncardwell@...gle.com> wrote:
>
> On Mon, Aug 15, 2022 at 8:30 PM Jie Meng <jmeng@...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@...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@...gle.com>
Acked-by: Yuchung Cheng <ycheng@...gle.com>
Would be great to have a companion patch on SYN timeout as well.

>
> neal