netdev - Re: [PATCH net-next 3/4] tcp: simplify tcp_set_congestion

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Date:   Wed, 9 Sep 2020 23:17:21 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>, Kevin Yang <yyd@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Lawrence Brakmo <brakmo@...com>
Subject: Re: [PATCH net-next 3/4] tcp: simplify tcp_set_congestion_control():
 always reinitialize

On Wed, Sep 9, 2020 at 8:29 PM Martin KaFai Lau <kafai@...com> wrote:
>
> On Wed, Sep 09, 2020 at 02:15:55PM -0400, Neal Cardwell wrote:
> > Now that the previous patches ensure that all call sites for
> > tcp_set_congestion_control() want to initialize congestion control, we
> > can simplify tcp_set_congestion_control() by removing the reinit
> > argument and the code to support it.
> >
> > Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> > Acked-by: Yuchung Cheng <ycheng@...gle.com>
> > Acked-by: Kevin Yang <yyd@...gle.com>
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Cc: Lawrence Brakmo <brakmo@...com>
> > ---
> >  include/net/tcp.h   |  2 +-
> >  net/core/filter.c   |  3 +--
> >  net/ipv4/tcp.c      |  2 +-
> >  net/ipv4/tcp_cong.c | 11 ++---------
> >  4 files changed, 5 insertions(+), 13 deletions(-)
> >
> > diff --git a/include/net/tcp.h b/include/net/tcp.h
> > index e85d564446c6..f857146c17a5 100644
> > --- a/include/net/tcp.h
> > +++ b/include/net/tcp.h
> > @@ -1104,7 +1104,7 @@ void tcp_get_available_congestion_control(char *buf, size_t len);
> >  void tcp_get_allowed_congestion_control(char *buf, size_t len);
> >  int tcp_set_allowed_congestion_control(char *allowed);
> >  int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
> > -                            bool reinit, bool cap_net_admin);
> > +                            bool cap_net_admin);
> >  u32 tcp_slow_start(struct tcp_sock *tp, u32 acked);
> >  void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked);
> >
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index b26c04924fa3..0bd0a97ee951 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -4451,8 +4451,7 @@ static int _bpf_setsockopt(struct sock *sk, int level, int optname,
> >                       strncpy(name, optval, min_t(long, optlen,
> >                                                   TCP_CA_NAME_MAX-1));
> >                       name[TCP_CA_NAME_MAX-1] = 0;
> > -                     ret = tcp_set_congestion_control(sk, name, false,
> > -                                                      true, true);
> > +                     ret = tcp_set_congestion_control(sk, name, false, true);
> >               } else {
> >                       struct inet_connection_sock *icsk = inet_csk(sk);
> >                       struct tcp_sock *tp = tcp_sk(sk);
> > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > index 7360d3db2b61..e58ab9db73ff 100644
> > --- a/net/ipv4/tcp.c
> > +++ b/net/ipv4/tcp.c
> > @@ -3050,7 +3050,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level, int optname,
> >               name[val] = 0;
> >
> >               lock_sock(sk);
> > -             err = tcp_set_congestion_control(sk, name, true, true,
> > +             err = tcp_set_congestion_control(sk, name, true,
> >                                                ns_capable(sock_net(sk)->user_ns,
> >                                                           CAP_NET_ADMIN));
> >               release_sock(sk);
> > diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
> > index d18d7a1ce4ce..a9b0fb52a1ec 100644
> > --- a/net/ipv4/tcp_cong.c
> > +++ b/net/ipv4/tcp_cong.c
> > @@ -341,7 +341,7 @@ int tcp_set_allowed_congestion_control(char *val)
> >   * already initialized.
> >   */
> >  int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
> > -                            bool reinit, bool cap_net_admin)
> > +                            bool cap_net_admin)
> >  {
> >       struct inet_connection_sock *icsk = inet_csk(sk);
> >       const struct tcp_congestion_ops *ca;
> > @@ -365,15 +365,8 @@ int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
> >       if (!ca) {
> >               err = -ENOENT;
> >       } else if (!load) {
> nit.
>
> I think this "else if (!load)" case can be completely removed and simply
> allow it to fall through to the last
> "else { tcp_reinit_congestion_control(sk, ca); }" .

Thanks, Martin. That is a very nice observation, and I think you are
right that we can make the additional refactor/simplification/clean-up
that you mention, without changing behavior. For clarity I think that
would be nice to have as a separate follow-on commit. Are you
interested in posting a follow-on patch for that, since it's your nice
idea?

thanks,
neal