[openib-general] basic IB doubt

[Ralph Campbell]

On Wed, 2006-08-23 at 14:00 -0500, Tang, Changqing wrote:
> Thanks for all your replies. So my general question is, why only 4bytes
> immediate data can
> Generate completion event on B side, Why RDMA-write with any data size
> does not generate
> A completion event on B side? basic there are the same thing, the only
> different is, one
> Copy 4bytes to completion structure, the other copy all data to provided
> dest buffer.
> 
> --CQ

This is just the way IB was defined.
Both RDMA write and RDMA write with immediate transfer
up to 2 Gigabytes of data to the destination address.
The latter just signals node B that the operation
is complete and the former doesn't.  Node B can use
the immediate data as a hint to which RDMA operation
just completed.