[Mesa-dev] i965: Use isl for hiz and stencil

[Jason Ekstrand]

On Mon, May 8, 2017 at 11:10 PM, Pohjolainen, Topi <
topi.pohjolainen at gmail.com> wrote:

> On Mon, May 08, 2017 at 04:51:35PM -0700, Jason Ekstrand wrote:
> > On Wed, May 3, 2017 at 2:22 AM, Topi Pohjolainen <
> topi.pohjolainen at gmail.com
> > > wrote:
> >
> > > Patches 1-17 are revision that
> > >
> > >   - rework hiz on gen6 to use on-demand offset calculator allowing
> > >     one to drop dependency to miptree structure and
> > >   - rework all auxiliary surfaces to be created against isl directly.
> > >
> > > Patches 18 and 19 introduce new surface layout in ISL. This is called
> > > back-to-back and similar to layout ALL_SLICES_AT_EACH_LOD found in
> > > i965 for gen6 hiz and stencil. This layout stacks slices for each level
> > > after one and other, or back to back. All slices ate each lod is almost
> > > the same except that it places levels one and two side-by-side trying
> > > to preserve space. Back-to-back wastes a little more memory but aligns
> > > each level on page boundary simplifying driver logic.
> > >
> >
> > My primary gripe here is that you seem to have half-added back-to-back to
> > ISL.  If this layout is a long-term thing, then we should add a new
> > ISL_DIM_LAYOUT_GEN6_BACK_TO_BACK layout and plumb your offset function
> > through isl_surf_get_image_offset_sa.  Is this intended to be a permanent
> > solution?  I think eventually, I'd like us to go with one surf per
> miplevel
> > (which is almost the same) but I can see how this is easier at the
> moment.
> > However, I think this works sufficiently well that I'm ok with doing the
> > back-to-back thing for a while.
>
> I thought about adding new layout type but couldn't decide which way is
> better. It is easy to buy your arguments in favor, and I'm happy to give it
> a go.
> If miptree per level is your number one choice, then lets go with that.


I said "one surf per miplevel".  I see no reason why we need N miptrees.


> I just
> need to check a few things first about the actual solution. I would see
> something in these lines:
>
> 1) Add a dynamically allocated array of miptrees into miptree. This would
>    contain miptree instance per level.
>
> 2) Still uses one buffer object containing space for all levels. The
> instances
>    in the array would either have their ::bo pointer zero or pointing to
> the
>    parent ::bo. In both cases ::offset would point the start of the level.
>

Yes


> 3) Instances in the array are not reference counted and therefore deleted
>    simply by deallocating the malloced chunk underneath.
>

If we have one isl_surf per miplevel and not a miptree per level, then I
don't think this is an issue.


> 4) Add similar dynamically allocated array of intel_miptree_aux_buffer
>    instances for hiz. Here also use one ::bo which would need to added to
>    miptree I think cause there ins't one in miptree. Or perhaps add the
>    array of aux buffers to aux buffer?
>

Looking at intel_miptree_aux_buffer, I think what we would end up with is
an array of aux_buffers


> 5) ISL doesn't need to know about this and hence we would add the total
> space
>    calculator along with ::offset initialization in i965 (brw_tex_layout,
>    I think).
>

That's fine.  We already do that in Vulkan with anv_surface.  ::offset
calculation can be done easily enough by just adding sizes.


> 6) In Vulkan <-> GL interop, we'd pass single level arrays only as ISL
> didn't
>    know about back-2-back. Or we simply don't care about gen6 as Vulkan
>    doesn't support it anyhow?
>

Yeah, we don't care about gen6.

--Jason
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