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

[Dave Airlie]

On Fri, 11 Sep 2020 at 22:27, Joonas Lahtinen
<joonas.lahtinen at linux.intel.com> wrote:
>
> + 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.
>

Oops thanks for enlightenment! Indeed binding things to the GTT
properly helps, sg iterator I had produced wrong pte entries, now I
can at least see an X stipple.

Dave.