Just wanted to float an idea we are thinking about. It builds on the basic idea of what Intel submitted as their RV module [1]. This however does things a bit differently and is really all about bulk zero-copy using the kernel. It is a new ULP. The major differences are that there will be no new cdev needed. We will make use of the existing HFI1 cdev where an FD is needed. We also propose to make use of IO-Uring (hence needing FD) to get requests into the kernel. The idea will be to not share Uverbs objects with the kernel. The kernel will maintain ownership of the qp, pd, mr, cq, etc. Connections we envision to be maintained by the kernel using RDMA CM. Similar in fashion to how RDS or IPoIB works. This of course means an RC QP which allows our TID RDMA feature to work under the hood. We have looked into RDS and RTRS and both seem to be the wrong interface. RDS provides a lot of what we are looking for but it seems to be a bit overkill and has higher overhead than we hope to achieve. Performance results show it to be less performant than direct to verbs. After reviewing the RV submission, I don't think there is any reason to try to revamp that submission. It seems to be very tightly tied to PSM3 whereas this is meant to be more generic. At this point we are interested in what questions you would have or opinions. We would like to get some feedback early in the process. As we develop the code we'll continue to post, similar to how we did rdmavt and welcome anyone that wants to collaborate. [1] https://lore.kernel.org/linux-rdma/20210319125635.34492-1-kaike.wan@xxxxxxxxx/ -Denny
