netdev - Re: [RFC 2/2] net: bridge: add a software fast-path implementation

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Message-ID: <928253ff-7254-b8bb-20a7-ec12ad82e14d@nbd.name>
Date:   Tue, 29 Mar 2022 13:07:37 +0200
From:   Felix Fietkau <nbd@....name>
To:     Nikolay Aleksandrov <razor@...ckwall.org>, netdev@...r.kernel.org
Subject: Re: [RFC 2/2] net: bridge: add a software fast-path implementation


On 28.03.22 20:20, Nikolay Aleksandrov wrote:
> On 28/03/2022 18:15, Felix Fietkau wrote:
>> 
>> Hi Nik,
>> 
>> I'd like to follow up on our discussion regarding bridge offloading.
>> I managed to come up with a user space + eBPF implementation that replaces this code and shows mostly the same performance gain as my previous kernel space implementation.
>> 
>> At first I tried to use generic XDP, but after getting it working, performance was pretty bad (due to headroom issues) and I was told that this is by design and nobody should use it in production.
>> 
>> Then I reworked the code to use tc classifier instead and it worked much better.
>> 
>> It's not fully ready yet, I need to add some more tests for incompatible features, but I'm getting there...
>> The code is here: https://github.com/nbd168/bridger
>> 
>> There's one thing I haven't been able to figure out yet: What's the proper way to keep bridge fdb entries alive from user space without modifying them in any other way?
>> 
>> - Felix
> 
> Hi Felix,
> That's very nice! Interesting work. One way it's usually done is through periodic NTF_USE (refresh),
> another would be to mark them externally learned and delete them yourself (user-space aging).
> It really depends on the exact semantics you'd like.
I will try NTF_USE, thanks. I really just want to keep the bridge fdb 
entries alive while there is activity on the offloaded flows.

- Felix