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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 02:17 UTC

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From: Joe Touch <touch@strayalpha.com>
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Date: Mon, 01 Jul 2019 19:16:59 -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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Oh, I should mention why this was an assumption - it allows RDMA-style direct data placement and zero-copy reassembly in the fast-path (happy order) case.

That’s not possible without copies otherwise.

Further, in the most typical expected case of two fragments, it enables zero-copy for the first fragment, which could more than halve the copies even if later fragments are put in holding areas.

Joe

> On Jul 1, 2019, at 6:55 PM, Joe Touch <touch@strayalpha.com> wrote:
> 
> 
> 
>> On Jul 1, 2019, at 5:42 PM, C. M. Heard <heard@pobox.com> wrote:
>> 
>> The original complaint was:
>> 
>>> The solution below doesn't appear to avoid copying/moving large amounts
>>> of data.
>>> 
>>> At a minimum, can you address #2? If we can do this without moving
>>> around a lot of data, it might be viable.
>> 
>> I believe I've addressed that point.
> 
> The assumption was ‘to place the fragments in order using existing efficiencies,’ which assumed the data starts at the beginning of the conventional UDP area in each fragment. That’s what LITE+FRAG does.. You need to copy to achieve that.
> 
> Joe
> 
> 
>

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