netdev - Re: [RFC PATCH v2 bpf-next 00/15] xdp

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Message-ID: <87wocqrz2v.fsf@toke.dk>
Date:   Sun, 27 Oct 2019 16:24:24 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Toshiaki Makita <toshiaki.makita1@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Pravin B Shelar <pshelar@....org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        William Tu <u9012063@...il.com>,
        Stanislav Fomichev <sdf@...ichev.me>
Subject: Re: [RFC PATCH v2 bpf-next 00/15] xdp_flow: Flow offload to XDP

Toshiaki Makita <toshiaki.makita1@...il.com> writes:

> On 19/10/23 (水) 2:45:05, Toke Høiland-Jørgensen wrote:
>> John Fastabend <john.fastabend@...il.com> writes:
>> 
>>> I think for sysadmins in general (not OVS) use case I would work
>>> with Jesper and Toke. They seem to be working on this specific
>>> problem.
>> 
>> We're definitely thinking about how we can make "XDP magically speeds up
>> my network stack" a reality, if that's what you mean. Not that we have
>> arrived at anything specific yet...
>> 
>> And yeah, I'd also be happy to discuss what it would take to make a
>> native XDP implementation of the OVS datapath; including what (if
>> anything) is missing from the current XDP feature set to make this
>> feasible. I must admit that I'm not quite clear on why that wasn't the
>> approach picked for the first attempt to speed up OVS using XDP...
>
> Here's some history from William Tu et al.
> https://linuxplumbersconf.org/event/2/contributions/107/
>
> Although his aim was not to speed up OVS but to add kernel-independent 
> datapath, his experience shows full OVS support by eBPF is very
> difficult.

Yeah, I remember seeing that presentation; it still isn't clear to me
what exactly the issue was with implementing the OVS datapath in eBPF.
As far as I can tell from glancing through the paper, only lists program
size and lack of loops as limitations; both of which have been lifted
now.

The results in the paper also shows somewhat disappointing performance
for the eBPF implementation, but that is not too surprising given that
it's implemented as a TC eBPF hook, not an XDP program. I seem to recall
that this was also one of the things puzzling to me back when this was
presented...

-Toke