netdev - Re: [PATCH v3] tcp: Use BPF timeout setting for SYN ACK RTO

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Message-ID: <CADVnQymw1A18bgGX=ujOmsVijQrfvSSnmtwRAqdx_JWCeNnvnw@mail.gmail.com>
Date:   Wed, 3 Nov 2021 17:53:08 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Yuchung Cheng <ycheng@...gle.com>
Cc:     Akhmat Karakotov <hmukos@...dex-team.ru>, kafai@...com,
        brakmo@...com, eric.dumazet@...il.com, mitradir@...dex-team.ru,
        netdev@...r.kernel.org, zeil@...dex-team.ru
Subject: Re: [PATCH v3] tcp: Use BPF timeout setting for SYN ACK RTO

On Wed, Nov 3, 2021 at 5:23 PM Yuchung Cheng <ycheng@...gle.com> wrote:
>
> On Wed, Nov 3, 2021 at 1:46 PM Akhmat Karakotov <hmukos@...dex-team.ru> wrote:
> >
> > When setting RTO through BPF program, some SYN ACK packets were unaffected
> > and continued to use TCP_TIMEOUT_INIT constant. This patch adds timeout
> > option to struct request_sock. Option is initialized with TCP_TIMEOUT_INIT
> > and is reassigned through BPF using tcp_timeout_init call. SYN ACK
> > retransmits now use newly added timeout option.
> >
> > Signed-off-by: Akhmat Karakotov <hmukos@...dex-team.ru>
> > ---
> >  include/net/request_sock.h      |  2 ++
> >  include/net/tcp.h               |  2 +-
> >  net/ipv4/inet_connection_sock.c |  4 +++-
> >  net/ipv4/tcp_input.c            |  8 +++++---
> >  net/ipv4/tcp_minisocks.c        | 12 +++++++++---
> >  5 files changed, 20 insertions(+), 8 deletions(-)
> >
> > diff --git a/include/net/request_sock.h b/include/net/request_sock.h
> > index 29e41ff3ec93..144c39db9898 100644
> > --- a/include/net/request_sock.h
> > +++ b/include/net/request_sock.h
> > @@ -70,6 +70,7 @@ struct request_sock {
> >         struct saved_syn                *saved_syn;
> >         u32                             secid;
> >         u32                             peer_secid;
> > +       u32                             timeout;
> >  };
> >
> >  static inline struct request_sock *inet_reqsk(const struct sock *sk)
> > @@ -104,6 +105,7 @@ reqsk_alloc(const struct request_sock_ops *ops, struct sock *sk_listener,
> >         sk_node_init(&req_to_sk(req)->sk_node);
> >         sk_tx_queue_clear(req_to_sk(req));
> >         req->saved_syn = NULL;
> > +       req->timeout = 0;
> >         req->num_timeout = 0;
> >         req->num_retrans = 0;
> >         req->sk = NULL;
> > diff --git a/include/net/tcp.h b/include/net/tcp.h
> > index 3166dc15d7d6..e328d6735e38 100644
> > --- a/include/net/tcp.h
> > +++ b/include/net/tcp.h
> > @@ -2323,7 +2323,7 @@ static inline u32 tcp_timeout_init(struct sock *sk)
> >
> >         if (timeout <= 0)
> >                 timeout = TCP_TIMEOUT_INIT;
> > -       return timeout;
> > +       return min_t(int, timeout, TCP_RTO_MAX);
> >  }
> >
> >  static inline u32 tcp_rwnd_init_bpf(struct sock *sk)
> > diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> > index 0d477c816309..cdf16285e193 100644
> > --- a/net/ipv4/inet_connection_sock.c
> > +++ b/net/ipv4/inet_connection_sock.c
> > @@ -870,7 +870,9 @@ static void reqsk_timer_handler(struct timer_list *t)
> >
> >                 if (req->num_timeout++ == 0)
> >                         atomic_dec(&queue->young);
> > -               timeo = min(TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
> > +               timeo = min_t(unsigned long,
> > +                             (unsigned long)req->timeout << req->num_timeout,
> > +                             TCP_RTO_MAX);
>
> would it make sense to have a helper tcp_timeout_max() to reduce
> clutter? but that can be done by a later refactor patch

I like Yuchung's idea to have a helper function (perhaps
reqsk_timeout() to go with reqsk_timer_handler()?)  to calculate the
timeout value, since there are 3 of these non-trivial expressions.
Otherwise this looks good to me.

thanks,
neal