netdev - Re: [PATCH net-next 0/4] tcp: increase flexibility of EBPF congestion control initialization

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Date:   Wed, 9 Sep 2020 23:21:50 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     David Miller <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 0/4] tcp: increase flexibility of EBPF congestion
 control initialization

On Wed, Sep 9, 2020 at 8:36 PM Martin KaFai Lau <kafai@...com> wrote:
>
> On Wed, Sep 09, 2020 at 02:15:52PM -0400, Neal Cardwell wrote:
> > 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.
> Thanks for this work.  Only have one nit in patch 3 for consideration.
>
> Acked-by: Martin KaFai Lau <kafai@...com>

Thanks for the review! I like your suggestion in patch 3 to further
simplify the code. Do you mind submitting your idea for a follow-on
clean-up/refactor as a separate follow-on commit?

thanks,
neal