Hi Dennis,

just as a wild idea, would be an option to use the SMB-Direct [1] protocol defined here?

It basically provides a stream/packet like transport based on IB_WR_SEND[_WITH_INV]
and in addition it allows direct memory transfers with IB_WR_RDMA_READ or IB_WR_RDMA_WRITE.

It's called SMB-Direct as it's currently used as a transport for the SMB3 protocol,
but it could also be used as transport for other things.

Over the last years I've been working on a PF_SMBDIRECT socket driver [2]
as a hobby project in order to support it for Samba. It's not yet production ready
and has known memory leaks, but the basics already work. The api [3] is based on
sendmsg/recvmsg with using MSG_OOB with msg->msg_control for direct memory transfers.
I'll actually use it with IORING_OP_SENDMSG and IORING_OP_RECVMSG, which allow msg->msg_control
starting 5.12 kernels.

metze

[1] https://winprotocoldoc.blob.core.windows.net/productionwindowsarchives/MS-SMBD/%5bMS-SMBD%5d.pdf
[2] https://git.samba.org/?p=metze/linux/smbdirect.git;a=summary
[3] https://git.samba.org/?p=metze/linux/smbdirect.git;a=blob;f=smbdirect.h;hb=refs/heads/smbdirect-work-in-progress


Am 19.08.21 um 21:09 schrieb Dennis Dalessandro:

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@intel.com/ (local)

-Denny