[Intel-gfx] dg1 flag for userspace to allocate contig resources

[Joonas Lahtinen]

+ Jani and Ville

Quoting Matthew Auld (2020-09-11 11:56:56)
> On 11/09/2020 06:42, Dave Airlie wrote:
> > I've just been looking at the current DG1 uapi, and I can't see any
> > flag to allow userspace to upfront say it was a contiguous vram BO.
> > 
> > I think you'd really want this for scanout, since otherwise you'll
> > have to migrate any non-contig to contig when it transitions to
> > scanout, and cause an extra set of copies.
> 
> Hmm, why do we need physically contiguous memory for scanout? From hw 
> pov it's seen through the GTT.

That's correct. On both discrete (and integrated) platforms the scan-out
addresses on Intel GPUs are programmed to targer Global GTT managed by
kernel. So no need to have the backing storage contiguous.

Only extra action required for a scan-out BO is to bind it to the GGTT in
addition to the ppGTT that renders to it. 

GGTT is relatively expensive to write to these days and limited in size,
but that can't really be helped with an upfront flag.

Regards, Joonas