[Mesa-dev] [PATCH 01/14] i965: Don't tile 1D miptrees.

[Neil Roberts]

I made a similar patch in my local tree because it will be necessary for
Skylake which doesn't support tiling for 1D textures. I made a little
test to time rendering a large (4096) 1D texture here:

https://github.com/bpeel/glthing/tree/time-1d-texture

It gives about an 11% increase in FPS with this patch.

It seems like a good idea to me to make it check the height rather than
the texture dimensions as Kenneth says.

Regards,
- Neil

Kenneth Graunke <kenneth at whitecape.org> writes:

> On Saturday, February 07, 2015 02:46:31 AM Francisco Jerez wrote:
>> Kenneth Graunke <kenneth at whitecape.org> writes:
>> 
>> > On Friday, February 06, 2015 07:23:15 PM Francisco Jerez wrote:
>> >> It doesn't really improve locality of texture fetches, quite the
>> >> opposite it's a waste of memory bandwidth and space due to tile
>> >> alignment.
>> >> ---
>> >>  src/mesa/drivers/dri/i965/intel_mipmap_tree.c | 4 ++++
>> >>  1 file changed, 4 insertions(+)
>> >> 
>> >> diff --git a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
>> >> index 64752dd..311b204 100644
>> >> --- a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
>> >> +++ b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
>> >> @@ -488,6 +488,10 @@ intel_miptree_choose_tiling(struct brw_context *brw,
>> >>         base_format == GL_DEPTH_STENCIL_EXT)
>> >>        return I915_TILING_Y;
>> >>  
>> >> +   if (mt->target == GL_TEXTURE_1D ||
>> >> +       mt->target == GL_TEXTURE_1D_ARRAY)
>> >> +      return I915_TILING_NONE;
>> >> +
>> >>     int minimum_pitch = mt->total_width * mt->cpp;
>> >>  
>> >>     /* If the width is much smaller than a tile, don't bother tiling. */
>> >> 
>> >
>> > What do you think about checking mt->logical_height0 == 1 instead?
>> > GLES doesn't have 1D textures, but people might use a 2D texture with
>> > height 1, and I think the same logic applies.
>> >
>> > I've also been thinking of trying to make core Mesa hide 1D textures and
>> > simply turn them into 2D textures with height = 1, so drivers don't have
>> > to deal with them.
>> >
>> > Either way, this seems like a good idea to me.
>> 
>> I guess that would work because the layer count of 1D array textures
>> ends up in logical_depth0 rather than logical_height0?  Sounds good to
>> me, but it would also have the side effect of not tiling "degenerate" 3D
>> textures with height=1 but depth>1, I guess we would still like to tile
>> those?  How about (mt->logical_height0 == 1 && (mt->logical_depth0 == 1 ||
>> mt->target != GL_TEXTURE_3D))?
>> 
>> Thanks Ken!
>
> I suppose that's fine, though frankly, trying to optimize a texture with
> height 1 at all seems pretty unnecessary to me.  I've never seen a 3D
> texture with height 1 in the wild...
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