Subject: Re: [RFC PATCH v2 bpf-next 00/15] xdp_flow: Flow offload to XDP

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Thu, 31 Oct 2019 13:12:07 +0100

Toshiaki Makita <[email-masked]> writes:

> On 2019/10/28 0:21, Toke Høiland-Jørgensen wrote:
>> Toshiaki Makita <[email-masked]> writes:
>>>> Yeah, you are right that it's something we're thinking about. I'm not
>>>> sure we'll actually have the bandwidth to implement a complete solution
>>>> ourselves, but we are very much interested in helping others do this,
>>>> including smoothing out any rough edges (or adding missing features) in
>>>> the core XDP feature set that is needed to achieve this :)
>>>
>>> I'm very interested in general usability solutions.
>>> I'd appreciate if you could join the discussion.
>>>
>>> Here the basic idea of my approach is to reuse HW-offload infrastructure
>>> in kernel.
>>> Typical networking features in kernel have offload mechanism (TC flower,
>>> nftables, bridge, routing, and so on).
>>> In general these are what users want to accelerate, so easy XDP use also
>>> should support these features IMO. With this idea, reusing existing
>>> HW-offload mechanism is a natural way to me. OVS uses TC to offload
>>> flows, then use TC for XDP as well...
>> 
>> I agree that XDP should be able to accelerate existing kernel
>> functionality. However, this does not necessarily mean that the kernel
>> has to generate an XDP program and install it, like your patch does.
>> Rather, what we should be doing is exposing the functionality through
>> helpers so XDP can hook into the data structures already present in the
>> kernel and make decisions based on what is contained there. We already
>> have that for routing; L2 bridging, and some kind of connection
>> tracking, are obvious contenders for similar additions.
>
> Thanks, adding helpers itself should be good, but how does this let users
> start using XDP without having them write their own BPF code?

It wouldn't in itself. But it would make it possible to write XDP
programs that could provide the same functionality; people would then
need to run those programs to actually opt-in to this.

For some cases this would be a simple "on/off switch", e.g.,
"xdp-route-accel --load <dev>", which would install an XDP program that
uses the regular kernel routing table (and the same with bridging). We
are planning to collect such utilities in the xdp-tools repo - I am
currently working on a simple packet filter:
https://github.com/xdp-project/xdp-tools/tree/xdp-filter

For more advanced use cases (such as OVS), the application packages will
need to integrate and load their own XDP support. We should encourage
that, and help smooth out any rough edges (such as missing features)
needed for this to happen.

-Toke