netdev - Re: [PATCH bpf-next 09/13] bpf: Add BPF_FUNC

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Date:   Mon, 16 Dec 2019 23:08:56 +0000
From:   Alexei Starovoitov <ast@...com>
To:     Martin Lau <kafai@...com>, Eric Dumazet <eric.dumazet@...il.com>
CC:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Kernel Team <Kernel-team@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 09/13] bpf: Add BPF_FUNC_jiffies

On 12/16/19 11:14 AM, Martin Lau wrote:
> At least for bpf_dctcp.c, I did not expect it could be that close to tcp_dctcp.c
> when I just started converted it.  tcp_cubic/bpf_cubic still has some TBD
> on jiffies/msec.
> 
> Agree that it is beneficial to have one copy.   It is likely
> I need to make some changes on the tcp_*.c side also.  Hence, I prefer
> to give it a try in a separate series, e.g. revert the kernel side
> changes will be easier.

I've looked at bpf_cubic.c and bpf_dctcp.c as examples of what this
patch set can do. They're selftests of the feature.
What's the value of keeping them in sync with real kernel cc-s?
I think it's fine if they quickly diverge.
The value of them as selftests is important though. Quite a bit of BTF
and verifier logic is being tested.
May be add a comment saying that bpf_cubic.c is like cubic, but doesn't
have to be exactly cubic ?