[mvapich-discuss] Re: data placement in-order guarantee ?

[अनुज]

On Tue, Feb 2, 2010 at 9:35 PM, Håkon Bugge <Haakon.Bugge at sun.com> wrote:

> On Feb 2, 2010, at 16:14 , yogeshwar sonawane wrote:
>
> > Hi all,
> >
> > Following question can be of naïve nature. Kindly, help me to clarify
> > the points.
> > Thanks in Advance.
> >
> > [snip].
> >
> > It will be helpful if some information is shared as how mvapich2
> > handles the situation regarding above point (while using rdma
> > operations) ?
>
> Snip from the InfiniBandTM Architecture Specification:
>
> o9-20: An application shall not depend of the contents of an RDMA WRITE
> buffer at the responder until one of the following has occurred:
> 19 20 21
> •       Arrival and Completion of the last RDMA WRITE request packet when
> used with Immediate data.
> •       Arrival and completion of a subsequent SEND message.
> •       Update of a memory element by a subsequent ATOMIC operation.
>
> Now, most MPI implementation does not obey this; IIRC MVAPICH does rely on
> the last byte (word?) being written after all other payload,


But MVAPICH assumes last byte is written in last. What if that is not the
case?


> Scali MPI relies on 4-byte write atomicy and uses a special
> encoding/decoding which sustains any reordering of the payload (as long as
> each 4-byte word is written as an atomic unit). The benefit, besides
> robustness, is the capability of a worm-hole message consumption (the
> message can be decoded and copied into the MPI user buffer _before_ it has
> been fully received). This method is currently a patent application, so I do
> not recommend you to copy-cat this method.
>

Can u provide a link for this method? Atleast I can go through some details
of this technique.

>
> So your choice is to be a "nice guy" using one of the preferred methods
> from the IB standard or rely on how different IB _implementations_ work.
>
>
>
> Håkon
>
>
>
>
> >
> > I thought that i should mail to both the mailing lists as topic covers
> > both domains.
> >
> > Thanks and Regards,
> > Yogeshwar
> > --
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>
> Håkon Bugge
> Haakon.bugge at Sun.com
> +47 924 84 514
>
>
>
> --
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>



-- 
Anuj Aggarwal

.''`.
: :Ⓐ :   # apt-get install hakuna-matata
`. `'`
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