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From: Justin Iurman <justin.iurman@uliege.be>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: netdev@vger.kernel.org, davem@davemloft.net, kuba@kernel.org,
	yoshfuji@linux-ipv6.org, dsahern@kernel.org, tom@herbertland.com
Subject: Re: [RFC net-next] ipv6: Attempt to improve options code parsing
Date: Tue, 3 Aug 2021 19:41:12 +0200 (CEST)	[thread overview]
Message-ID: <2112761850.30866431.1628012472544.JavaMail.zimbra@uliege.be> (raw)
In-Reply-To: <aa58193c-0a8f-d11b-fb0c-bc41571e33ac@gmail.com>

>>>> 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.

      reply	other threads:[~2021-08-03 17:41 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-02 20:51 Justin Iurman
2021-08-03 15:03 ` Eric Dumazet
2021-08-03 16:06   ` Justin Iurman
2021-08-03 16:35     ` Eric Dumazet
2021-08-03 17:41       ` Justin Iurman [this message]

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