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Re: [tsvwg] RDMA Support by UDP FRAG Option

Joseph Touch <touch@strayalpha.com> Thu, 17 June 2021 00:16 UTC

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From: Joseph Touch <touch@strayalpha.com>
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Date: Wed, 16 Jun 2021 17:16:44 -0700
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To: Tom Herbert <tom@herbertland.com>
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Subject: Re: [tsvwg] RDMA Support by UDP FRAG Option
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> On Jun 16, 2021, at 10:16 AM, Tom Herbert <tom@herbertland.com> wrote:
> 
>> ...
>> The idea is that the data can be placed directly in memory, with the last 3 bytes overwriting the first three. By moving only the space covered by the options, direct data placement can be used:
>> 
>> 123de - write up to the last 3 bytes
>> a23de - overwrite the last 3 bytes starting at the beginning (next 2 lines too)
> 
> That presumes that the memory holding the payload is writeable which
> is not always true. For instance, that would not be the case if the
> device DMAs the data into GPU memory.

This approach is already OBE and thus not relevant.

However, the approach above remains an expectation of any DMA transfer - there are always edge aspects that need to be adjusted, whether by a separate DMA or some other mechanism. It doesn’t have to be one byte at a time, as shown above.

Joe

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