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    SubjectRe: [RFC] Make use of non-dynamic dmabuf in RDMA
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    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?

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