linux-kernel - Re: [PATCH v3 net-next 00/12] bpf: rewrite value tracking in verifier

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Message-ID: <595C1685.4060209@iogearbox.net>
Date:   Wed, 05 Jul 2017 00:28:21 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Edward Cree <ecree@...arflare.com>,
        Alexei Starovoitov <ast@...com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        iovisor-dev <iovisor-dev@...ts.iovisor.org>
Subject: Re: [PATCH v3 net-next 00/12] bpf: rewrite value tracking in verifier

On 07/04/2017 09:22 PM, Edward Cree wrote:
> On 30/06/17 19:15, Alexei Starovoitov wrote:
>> On 6/30/17 9:44 AM, Edward Cree wrote:
>>> I haven't measured the test_progs ones, because I *still* haven't gotten
>>>   around to actually setting up a BPF toolchain (it doesn't help that I'm
>>>   building everything on a test server that gets reimaged every night to
>>>   run our nightly tests...).
>>
>> then you're missing a lot of tests then...
>> installing llvm is trivial. On x86 there are plenty of pre-built
>> packages that you can apt-get or yum.
>> Dave had to compile llvm and gcc from source on sparc, so volatile test
>> server isn't really an excuse to miss all these tests ;)
>> especially for such large verifier change.
>>
> After two days' wrestling with clang's build system, I'm finally able to
>   run test_progs, and all its tests pass as of the full patch series.

(Hmm, usually with major distros LLVM comes with BPF targets enabled
by default these days, so there's less need to compile it from scratch
actually, just installation via yum/apt/... would suffice then.)

> Here are the processed insn counts:
>
> Program         net-next  short  full
> test_pkt_access       78     79    79
> test_xdp             386    411   407
> test_l4lb           6438   4154  4154
> test_tcp_estats      435    436   435
> test_bpf_obj_id        8      8     8
> test_pkt_md_access    41     42    42
>
> "short" is the first 3 patches plus the 'roll back ptr&const' patch I
>   posted on Friday.  "full" is the full 12-patch series.  "Program" is
>   the function in test_progs.c.
> I don't know why test_l4lb has to process _fewer_ insns with my patches;
>   if anything I'm worrying that I may be incorrectly pruning branches.
> (I've spotted a possible bug in that I'm not looking at 'id' which,
>   although it doesn't have to match, if two regs in the old state had the
>   same id as each other, then those regs in the new state have to have
>   the same id as each other too.)
> Also interesting is that going from "short" to "full" only decreases the
>   counts, suggesting that the ptr&const and full negative/positive
>   tracking isn't (at least for these test cases) costly.

Have you tried with cilium's BPF code? The kernel selftests are quite small,
so not really pushing processed insns too far. I can send you a BPF obj file
if that's easier for testing.

Thanks,
Daniel