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Re: [tsvwg] RDMA Support by UDP FRAG Option

Tom Herbert <tom@herbertland.com> Thu, 17 June 2021 00:48 UTC

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From: Tom Herbert <tom@herbertland.com>
Date: Wed, 16 Jun 2021 17:48:21 -0700
Message-ID: <CALx6S37uN8TsXQZ3cv5jmxwxSyBRjK=-GQ_MsWxPWSs21XoGHw@mail.gmail.com>
To: Joseph Touch <touch@strayalpha.com>
Cc: TSVWG <tsvwg@ietf.org>
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Subject: Re: [tsvwg] RDMA Support by UDP FRAG Option
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On Wed, Jun 16, 2021, 5:16 PM Joseph Touch <touch@strayalpha.com> wrote:

>
>
> > 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.
>

What does OBE mean?

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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