Re: [PATCH RFC 2/3] RDMA/srp: Post command IUs inline

[sashiko-bot@kernel.org]

> srp_post_send() posts every information unit by reference, and the QP
> asks for no inline data. Before the HCA can send an SRP_CMD it
> therefore has to DMA-read the IU from host memory, and that read is
> on the latency path of every command.
> 
> Ask for SRP_MAX_INLINE_DATA bytes of inline data when creating the QP,
> enough for an SRP_CMD with an additional CDB and an indirect table of
> two descriptors (116 bytes). If the device refuses, ask for less. Intel
> irdma has a fixed limit of 216, 101 or 48 bytes, depending on the
> generation, and Alibaba erdma one of 96. On those devices, found by
> vendor ID, try these limits first, then step down 16 bytes at a time to
> none. libfabric's verbs provider also probes the inline limit by trial
> QP creation. The RDMA/CM and IB/CM QP creation paths move into
> srp_create_qp() so the retries cover both. Post an IU without immediate
> data with IB_SEND_INLINE when it fits in the inline size the device
> granted.
> 
> Providers copy inline data from sg_list[].addr as a kernel virtual
> address, so the inline path points iu->sge[0] at iu->buf.
> srp_post_send() resets it to iu->dma on every post, and iu->dma keeps
> the mapping.
> 
> Assisted-by: LLM
> Signed-off-by: Andrei-Alexandru Bleortu <me@andrei-z.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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