netdev - Re: [PATCH bpf-next v3 0/5] tcp: increase flexibility of EBPF congestion control initialization

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Message-ID: <CAADnVQJ8FnZEJ0fnODoRP-kKYsM4wj=H=cRx18DbEhgn=376Tw@mail.gmail.com>
Date:   Thu, 10 Sep 2020 21:20:28 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     Neal Cardwell <ncardwell.kernel@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        Neal Cardwell <ncardwell@...gle.com>,
        bpf <bpf@...r.kernel.org>, Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next v3 0/5] tcp: increase flexibility of EBPF
 congestion control initialization

On Thu, Sep 10, 2020 at 8:28 PM Martin KaFai Lau <kafai@...com> wrote:
>
> On Thu, Sep 10, 2020 at 03:35:31PM -0400, Neal Cardwell wrote:
> > From: Neal Cardwell <ncardwell@...gle.com>
> >
> > This patch series reorganizes TCP congestion control initialization so that if
> > EBPF code called by tcp_init_transfer() sets the congestion control algorithm
> > by calling setsockopt(TCP_CONGESTION) then the TCP stack initializes the
> > congestion control module immediately, instead of having tcp_init_transfer()
> > later initialize the congestion control module.
> >
> > This increases flexibility for the EBPF code that runs at connection
> > establishment time, and simplifies the code.
> >
> > This has the following benefits:
> >
> > (1) This allows CC module customizations made by the EBPF called in
> >     tcp_init_transfer() to persist, and not be wiped out by a later
> >     call to tcp_init_congestion_control() in tcp_init_transfer().
> >
> > (2) Does not flip the order of EBPF and CC init, to avoid causing bugs
> >     for existing code upstream that depends on the current order.
> >
> > (3) Does not cause 2 initializations for for CC in the case where the
> >     EBPF called in tcp_init_transfer() wants to set the CC to a new CC
> >     algorithm.
> >
> > (4) Allows follow-on simplifications to the code in net/core/filter.c
> >     and net/ipv4/tcp_cong.c, which currently both have some complexity
> >     to special-case CC initialization to avoid double CC
> >     initialization if EBPF sets the CC.
> >
> > changes in v2:
> >
> > o rebase onto bpf-next
> >
> > o add another follow-on simplification suggested by Martin KaFai Lau:
> >    "tcp: simplify tcp_set_congestion_control() load=false case"
> >
> > changes in v3:
> >
> > o no change in commits
> >
> > o resent patch series from @gmail.com, since mail from ncardwell@...gle.com
> >   stopped being accepted at netdev@...r.kernel.org mid-way through processing
> >   the v2 patch series (between patches 2 and 3), confusing patchwork about
> >   which patches belonged to the v2 patch series
> Acked-by: Martin KaFai Lau <kafai@...com>

Applied.

Martin, thanks for the review.

Neal, please keep Acks when you resubmit patches without changes in the future.
Also please follow up with a selftests/bpf based on test_progs to
cover new functionality.

Thanks