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Re: [tsvwg] UDP Options: on forcing the use of UDP CS=0 in connection with FRAG+LITE

Joe Touch <touch@strayalpha.com> Tue, 02 July 2019 00:06 UTC

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From: Joe Touch <touch@strayalpha.com>
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Date: Mon, 01 Jul 2019 17:06:03 -0700
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To: "C. M. Heard" <heard@pobox.com>
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Subject: Re: [tsvwg] UDP Options: on forcing the use of UDP CS=0 in connection with FRAG+LITE
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On Jul 1, 2019, at 3:42 PM, C. M. Heard <heard@pobox.com> wrote:

>> In the new proposal, there would be a potentially variable offset from the
>> head of each mbuf in the chain.
>> 
>> Those might have very different overheads…
> 
> YMMV, but I find that argument to be unconvincing. Any not conspicuously
> deficient mbuf design needs to be able to easily trim off variable length
> headers from the start of a packet (e.g., by having a starting offset), or
> else it would not be able to efficiently accommodate IP options/extension
> headers, TCP options, tunnel encapsulation headers, and so on.
> 
> Mike

That correlates with what I’ve seen in performance exactly though. 

The common case is fast; other cases not so much. Even the mbuf start offset from malloc start matters a bit (per measurements I did with MD5 in memory). 

Joe

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