Re: Fw: About FRMR vec and SRQ post recv

[Steve Wise <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>]

> I try getting a summary. Give some comments on the following
> sentences,please.
> For local side(A), where data to be transferred is placed.
> send or RDMA Read/Write operations.
> the sge array in one send wr pointed by sgl_list should have the same
> [lr]key.
> a) one send wr could send two arbitrary regions when using dma mr's
> [lr]ley or local_dma_lkey
> b) one send wr could 'not' send two arbitrary regions registered by
> two FRWRs seperately.


b) is not true. If you register these 2 regions separately, then you can
certainly send them in one send wr, each being an sge entry in the wr.


>
> For remote side(B), where data transferred will be placed.
> 2) RDMA Read/Write operations could put data to
> a) a single physical continous region registerd
> b) two or more regions with contstraints that they could be registerd
> by one FRWR.
> c) could not put data to two regions registerd by two FRWR sperately
> since in side A, ib_send_wr.wr.rdma should specify one group
> {rkey,addr} for remote destination region.


This is all correct: The sink (aka the target) of a write or read is a
single rkey/addr/len. So to have it place into two separate regions, you
would need them to have been registered via fastreg-mr and thus they
would have to adhere to the constraints of a fastreg-mr.


>
> and send/recv operatons can also put data to
> c) two or more arbitrary regions using dma mr. since send operation in
> side A do not need remote {addr,rkey} and recv operation in side B
> could post two arbitrary regions using dma mr's lkey or local_dma_lkey
> in a singel recv_wr.
>

This is correct also. incoming sends will be placed into recv buffers as
specified in the sg list for the recv wr.


>
> I want to transfer data from two arbitrary regions of A to two
> arbitrary regions of B for a single RDMA Read/Write operation
> originally.And it seems impossible now.
>

you'll have to issue multiple reads or writes...


Steve
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