From: SPDK [mailto:firstname.lastname@example.org] On Behalf Of Kumar, Amit1
Sent: Thursday, June 20, 2019 1:04 PM
Subject: [SPDK] RDMA in-line data transfer for host READ operations.
I was looking at the NVMe Data-in and Data-out flow for NVMeOF RDMA
transport, looks like SPDK is capable of handling in-capsule data (for Write
operations from the host) by pre-posting in-capsule data buffer SGL to RDMA
recv buffers. But, looks like SPDK doesn't use in-line data buffers while sending
response to the NVMe read commands from the host and eventually using
RDMA write to send the data, can someone please confirm whether my
observation is correct or not?
In the NVMe-oF specification, there is no in-capsule data on the completion side. The
target simply posts the data as an RDMA write, then sends the completion immediately by
using an RDMA send. There wouldn't be any performance advantage to stuffing the data
into the RDMA send command.
At the RDMA level there are some things like IBV_SEND_INLINE that may help with
performance in some cases, but that's not in-capsule data.
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