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Date:   Tue, 3 Aug 2021 19:41:12 +0200 (CEST)
From:   Justin Iurman <>
To:     Eric Dumazet <>
Subject: Re: [RFC net-next] ipv6: Attempt to improve options code parsing

>>>> As per Eric's comment on a previous patchset that was adding a new HopbyHop
>>>> option, i.e. why should a new option appear before or after existing ones in the
>>>> list, here is an attempt to suppress such competition. It also improves the
>>>> efficiency and fasten the process of matching a Hbh or Dst option, which is
>>>> probably something we want regarding the list of new options that could quickly
>>>> grow in the future.
>>>> Basically, the two "lists" of options (Hbh and Dst) are replaced by two arrays.
>>>> Each array has a size of 256 (for each code point). Each code point points to a
>>>> function to process its specific option.
>>>> Thoughts?
>>> Hi Justin
>>> I think this still suffers from indirect call costs (CONFIG_RETPOLINE=y),
>>> and eventually use more dcache.
>> Agree with both. It was the compromise for such a solution, unfortunately.
>>> Since we only deal with two sets/arrays, I would simply get rid of them
>>> and inline the code using two switch() clauses.
>> Indeed, this is the more efficient. However, we still have two "issues":
>>  - ip6_parse_tlv will keep growing and code could look ugly at some point
> Well, in 10 years there has not been a lot of growth.

Indeed, but I think it could grow a lot more in short/middle term. Just have a look at current discussions in the IETF (e.g., 6man) about HopbyHop limitations and anything related, as a way to widely improve their support and not just drop them. A better support could bring new options.

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