netdev - Re: [PATCH bpf-next v2 1/6] bpf: introduce BPF dispatcher

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Date:   Sun, 24 Nov 2019 18:16:07 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        bpf <bpf@...r.kernel.org>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Edward Cree <ecree@...arflare.com>,
        Toke Høiland-Jørgensen <thoiland@...hat.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Maxim Mikityanskiy <maximmi@...lanox.com>
Subject: Re: [PATCH bpf-next v2 1/6] bpf: introduce BPF dispatcher

On Sun, 24 Nov 2019 at 18:08, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Sun, Nov 24, 2019 at 07:55:07AM +0100, Björn Töpel wrote:
> > >
> > > I think I got it why it works.
> > > Every time the prog cnt goes to zero you free the trampoline right away
> > > and next time it will be allocated again and kzalloc() will zero selector.
> > > That's hard to spot.
> > > Also if user space does for(;;) attach/detach;
> > > it will keep stressing bpf_jit_alloc_exec.
> > > In case of bpf trampoline attach/detach won't be stressing it.
> > > Only load/unload which are much slower due to verification.
> > > I guess such difference is ok.
> > >
> >
> > Alexei, thanks for all feedback (on the weekend)! I agree with all of
> > above, and especially missing selftests and too much code duplication.
> >
> > I'll do a respin, but that'll be in the next window, given that Linus
> > will (probably) tag the release today.
>
> I want it to land just as much as you do :) Two weeks is not a big deal. We
> backport all of bpf and xdp as soon as it lands in bpf-next/net-next. We don't
> wait for patches to reach Linus's tree. So this dispatch logic will be running
> on our servers way sooner than you'd expect. I guess that explains my obsession
> with quality. Same goes for libbpf.
>

No reason to rush it in! It's just a week back and forth, and your
comments were spot on.


Cheers,
Björn


>