netdev - Re: [PATCH v8 bpf-next 0/7] bpf: tailcalls in BPF subprograms

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Date:   Wed, 23 Sep 2020 17:43:37 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Andrii Nakryiko <andriin@...com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH v8 bpf-next 0/7] bpf: tailcalls in BPF subprograms

On Wed, 23 Sep 2020 at 17:24, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
>
> On Wed, Sep 23, 2020 at 9:12 AM Lorenz Bauer <lmb@...udflare.com> wrote:
> >
> > On Fri, 18 Sep 2020 at 04:26, Alexei Starovoitov
> > <alexei.starovoitov@...il.com> wrote:
> > [...]
> > >
> > > Lorenz,
> > > if you can test it on cloudflare progs would be awesome.
> >
> > Our programs all bpf_tail_call from the topmost function, so no calls
> > from subprogs. I stripped out our FORCE_INLINE flag, recompiled and
> > ran our testsuite. cls_redirect.c (also in the kernel selftests) has a
> > test failure that I currently can't explain, but I don't have the time
> > to look at it in detail right now.
> >
>
> I've already converted test_cls_redirect.c in selftest to have
> __noinline variant. And it works fine. There are only 4 helper
> functions that can't be converted to a sub-program (pkt_parse_ipv4,
> pkt_parse_ipv6, and three buffer manipulation helpers) because they
> are accepting a pointer to a stack from a calling function, which
> won't work with subprograms. But all the other functions were
> trivially converted to __noinline and keep working.

Yeah, that is very possible. Keep in mind though that our internal
version has since become more complex, and also has a more
comprehensive test suite. I wasn't sounding the alarms, it's just an
FYI that I appreciate the work that went into this and have taken a
look, but that I need to do some more digging :)

-- 
Lorenz Bauer  |  Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK

www.cloudflare.com