Re: [Qemu-devel] [RfC PATCH 6/6] vfio/display: add dmabuf support (v15)

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> Looks pretty straight forward otherwise.  I like the LRU dmabuf
> freeing, but is it mostly for validating the interface?  My
> impression
> is that we'd reach a steady state with a single plane and single
> cursor so I wonder if keeping that cache really provides a noticeable
> benefit.

Really depends on what the guest is doing.  I didn't do too much
testing with various cache sizes and guests yet.

>   Perhaps for a Linux guest switching between vt and graphics
> mode?

fbcon/vt is one dmabuf.  xorg I have seen using multiple primary plane
dma-bufs, dunno why, doesn't change often.  wayland does page-flipping
on each rendered frame, which translates to very frequent dma-buf
changes and I expect the caching will pay off here.

cursor dma-buf with xorg changes each time the cursor shape changes.

>   It also seems like the primary and cursor will be fighting for
> the head of the list, so if we keep lists, maybe they should be per
> plane type.

Makes sense indeed.

> This uses the x-display option for now, how do we move past that to
> get
> automatic configuration?

I think a OnOffAuto display property would be the best choice.

cheers,
  Gerd