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

[Pohjolainen, Topi]

On Tue, May 09, 2017 at 08:45:55AM -0700, Jason Ekstrand wrote:
> 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.

Ah, right, my mistake. We need a little more than isl_surf instance though,
at least we need offset per level (unless we calculate that on-demand).
Of course we could use the current level/slice table but I'm hoping to get rid
of that.

> 
> 
> > 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