netdev - RE: [RFC PATCH bpf-next 0/3] Add a new bpf helper for FDB lookup

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Message-ID: <5f2492aedba05_54fa2b1d9fe285b42d@john-XPS-13-9370.notmuch>
Date:   Fri, 31 Jul 2020 14:52:46 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Yoshiki Komachi <komachi.yoshiki@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        KP Singh <kpsingh@...omium.org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        David Ahern <dsahern@...nel.org>
Cc:     Yoshiki Komachi <komachi.yoshiki@...il.com>,
        netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
        bpf@...r.kernel.org
Subject: RE: [RFC PATCH bpf-next 0/3] Add a new bpf helper for FDB lookup

Yoshiki Komachi wrote:
> This series adds a new bpf helper for doing FDB lookup in the kernel
> tables from XDP programs. This helps users to accelerate Linux bridge
> with XDP.
> 
> In the past, XDP generally required users to reimplement their own
> networking functionalities with specific manners of BPF programming
> by themselves, hindering its potential uses. IMO, bpf helpers to
> access networking stacks in kernel help to mitigate the programming
> costs because users reuse mature Linux networking feature more easily.
> 
> The previous commit 87f5fc7e48dd ("bpf: Provide helper to do forwarding
> lookups in kernel FIB table") have already added a bpf helper for access
> FIB in the kernel tables from XDP programs. As a next step, this series
> introduces the API for FDB lookup. In the future, other bpf helpers for
> learning and VLAN filtering will also be required in order to realize
> fast XDP-based bridge although these are not included in this series.

Just to clarify for myself. I expect that with just the helpers here
we should only expect static configurations to work, e.g. any learning
and/or aging is not likely to work if we do redirects in the XDP path.

Then next to get a learning/filtering/aging we would need to have a
set of bridge helpers to get that functionality as well? I believe
I'm just repeating what you are saying above, but wanted to check.

Then my next question is can we see some performance numbers? These
things are always trade-off between performance and ease of
use, but would be good to know roughly what we are looking at vs
a native XDP bridge functionality.

Do you have a use case for a static bridge setup? Nothing wrong to
stage things IMO if the 'real' use case needs learning and filtering.

I guess to get STP working you would minimally need learning and
aging?

Thanks,
John