Arlin> A very latency sensitive application that requires
Arlin> immediate notification of RDMA write completion on the
Arlin> remote node without ANY latency penalties associated with
Arlin> combining operations, HCA priority rules across QPs, wire
Arlin> congestion, etc. An application that has no requirement for
Arlin> messaging outside of remote rdma write completion
Arlin> notifications. The application would not have to register
Arlin> and manage additional message buffers on either side, we
Arlin> can just size the queues accordingly and post zero byte
Arlin> messages. We need something that would be equivelent to
Arlin> setting there polling on the last byte of inbound
Arlin> data. But, since data ordering within an operation is not
Arlin> guaranteed that is not an option. So, rdma with immediate
Arlin> data is the most optimal and simplistic method for
Arlin> indication of RDMA-write completion that we have available
Arlin> today. In fact, I would like to see it increased in size to
Arlin> make it even more useful.
Hmm. Can you put a number on how much better RDMA write with
immediate is on current HCA hardware? How does using the underlying
OpenIB verbs ability to post a list of work requests compare (ie
posting an RDMA write followed by a send in one verbs call)?
Maybe "post multiple" is a better direction for DAT.
- R.
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