Re: Enabling peer to peer device transactions for PCIe devices

Jason Gunthorpe
2017-01-05T19:01:13Z

On Thu, Jan 05, 2017 at 01:39:29PM -0500, Jerome Glisse wrote:

> 1) peer-to-peer because of userspace specific API like NVidia GPU
> direct (AMD is pushing its own similar API i just can't remember
> marketing name). This does not happen through a vma, this happens
> through specific device driver call going through device specific
> ioctl on both side (GPU and RDMA). So both kernel driver are aware
> of each others.

Today you can only do user-initiated RDMA operations in conjection
with a VMA.

We'd need a really big and strong reason to create an entirely new
non-VMA based memory handle scheme for RDMA.

So my inclination is to just completely push back on this idea. You
need a VMA to do RMA.

GPUs need to create VMAs for the memory they want to RDMA from, even
if the VMA handle just causes SIGBUS for any CPU access.

Jason