Hi,
I have been reading a lot of papers lately concerning high speed
networking, RDMA and storage networking over RDMA (iSER and SRP).
All papers state that buffers which are used in a RDMA transfer must be
"registered" first, so that they are "pinned down". This registration
has a significant cost, and the papers suggest various kinds of
solutions for this problem.
However, i cannot find any information why this registration is really
needed in the case of storage networking and why the cost of the
registration is so high. I am trying to understand why (or if) this
RDMA mechanism is different from regular DMA to for example a regular
SCSI controller.
Can anybody shed some light on this or point me to relevant information?
Thanks in advance.
Jos
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