On 18/08/2021 11:00, Christian König wrote: > Am 18.08.21 um 09:43 schrieb Gal Pressman: >> Hey all, >> >> Currently, the RDMA subsystem can only work with dynamic dmabuf >> attachments, which requires the RDMA device to support on-demand-paging >> (ODP) which is not common on most devices (only supported by mlx5). >> >> While the dynamic requirement makes sense for certain GPUs, some devices >> (such as habanalabs) have device memory that is always "pinned" and do >> not need/use the move_notify operation. >> >> The motivation of this RFC is to use habanalabs as the dmabuf exporter, >> and EFA as the importer to allow for peer2peer access through libibverbs. >> >> This draft patch changes the dmabuf driver to differentiate between >> static/dynamic attachments by looking at the move_notify op instead of >> the importer_ops struct, and allowing the peer2peer flag to be enabled >> in case of a static exporter. > > Well NAK to the general approach, this can be solved much easier. > > If you can't support dynamic moves while using the buffer then just pin all > buffers during import/export. > > This avoids the move notification and the framework/exporter can still correctly > account for pinned buffers. > > But please note that at least amdgpu never uses P2P support for pinned buffers > since we want to avoid that unmoveable buffers clutter video memory and create > conflicts with V4L and scanout. > > If you don't have such concerns in habanalabs then you can implement the pinning > there while keeping P2P still enabled. Thanks Christian! Are you suggesting to pass an empty move_notify callback instead of passing NULL? Also, doesn't the pin operation move the memory from the device to host memory?
