[Mesa-dev] [PATCH 04/14] i965/gen7: Don't allocate hiz miptree structure

[Jordan Justen]

On Fri, Jul 18, 2014 at 1:58 AM, Pohjolainen, Topi
<topi.pohjolainen at intel.com> wrote:
> On Tue, Jul 15, 2014 at 06:32:12PM -0700, Jordan Justen wrote:
>> We now skip allocating a hiz miptree for gen7. Instead, we calculate
>> the required hiz buffer parameters and allocate a bo directly.
>>
>> Signed-off-by: Jordan Justen <jordan.l.justen at intel.com>
>> ---
>>  src/mesa/drivers/dri/i965/intel_mipmap_tree.c | 95 ++++++++++++++++++++++++++-
>>  1 file changed, 93 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
>> index 8719c29..7e8bec8 100644
>> --- a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
>> +++ b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
>> @@ -823,7 +823,10 @@ intel_miptree_release(struct intel_mipmap_tree **mt)
>>        drm_intel_bo_unreference((*mt)->bo);
>>        intel_miptree_release(&(*mt)->stencil_mt);
>>        if ((*mt)->hiz_buf) {
>> -         intel_miptree_release(&(*mt)->hiz_buf->mt);
>> +         if ((*mt)->hiz_buf->mt)
>> +            intel_miptree_release(&(*mt)->hiz_buf->mt);
>> +         else
>> +            drm_intel_bo_unreference((*mt)->hiz_buf->bo);
>>           free((*mt)->hiz_buf);
>>        }
>>        intel_miptree_release(&(*mt)->mcs_mt);
>> @@ -1374,6 +1377,89 @@ intel_miptree_level_enable_hiz(struct brw_context *brw,
>>  }
>>
>>
>> +/**
>> + * Helper for intel_miptree_alloc_hiz() that determines the required hiz
>> + * buffer dimensions and allocates a bo for the hiz buffer.
>> + */
>> +static struct intel_miptree_aux_buffer *
>> +intel_gen7_hiz_buf_create(struct brw_context *brw,
>> +                          struct intel_mipmap_tree *mt)
>> +{
>> +   unsigned z_width = mt->logical_width0;
>> +   unsigned z_height = mt->logical_height0;
>> +   const unsigned z_depth = mt->logical_depth0;
>> +   unsigned hz_width, hz_height, qpitch;
>
> Minor nit, qpitch could be called hz_qpitch for clarity as it is a result of
> hiz-specific rules just as hz_width and hz_height. Simple matter of taste and
> you choose the way that you feel the best.
>
>> +   struct intel_miptree_aux_buffer *buf = calloc(sizeof(*buf), 1);
>> +
>> +   if (!buf)
>> +      return NULL;
>> +
>> +   /* Gen7 PRM Volume 2, Part 1, 11.5.3 "Hierarchical Depth Buffer" documents
>> +    * adjustments required for Z_Height and Z_Width based on multisampling.
>> +    */
>> +   switch(mt->num_samples) {
>> +   case 0:
>> +   case 1:
>> +      break;
>> +   case 2:
>> +   case 4:
>> +      z_width *= 2;
>> +      z_height *= 2;
>> +      break;
>> +   case 8:
>> +      z_width *= 4;
>> +      z_height *= 2;
>> +      break;
>> +   default:
>> +      assert(!"Unsupported sample count!");
>> +   }
>> +
>> +   const unsigned vertical_align = 8; /* 'j' in the docs */
>> +   const unsigned H0 = z_height;
>> +   const unsigned h0 = ALIGN(H0, vertical_align);
>> +   const unsigned h1 = ALIGN(minify(H0, 1), vertical_align);
>> +   const unsigned Z0 = z_depth;
>> +
>> +   /* HZ_Width (bytes) = ceiling(Z_Width / 16) * 16 */
>> +   hz_width = ALIGN(z_width, 16);
>> +
>> +   if (mt->target == GL_TEXTURE_3D) {
>> +      unsigned H_i = H0;
>> +      unsigned Z_i = Z0;
>> +      hz_height = 0;
>> +      for (int level = mt->first_level; level <= mt->last_level; ++level) {
>> +         unsigned h_i = ALIGN(H_i, vertical_align);
>> +         /* sum(i=0 to m; h_i * max(1, floor(Z_Depth/2**i))) */
>
> I had to think for a second if you had typo here (2**i) but then realized
> you used it to mean power-of-two. I've also seen people using 2^i, would that
> make sense to you?
>
>> +         hz_height += h_i * Z_i;
>> +         H_i = minify(H_i, 1);
>> +         Z_i = minify(Z_i, 1);
>> +      }
>> +      /* HZ_Height =
>> +       *    (1/2) * sum(i=0 to m; h_i * max(1, floor(Z_Depth/2**i)))
>> +       */
>> +      hz_height = CEILING(hz_height, 2);
>> +   } else {
>> +      qpitch = h0 + h1 + (12 * vertical_align);
>> +      /* HZ_Height (rows) = Ceiling ( ( Q_pitch * Z_depth/2) /8 ) * 8 */
>> +      hz_height = (ALIGN(qpitch, 8) / 2) * Z0;
>
> Here the ALIGN is no-op - qpitch is a sum of three already aligned numbers,
> and hence it is aligned itself. The final result in turn is not always aligned
> (althought is should be). For example, say
>
>   qpitch = ALIGN(16, 8) + ALIGN(minify(16, 1), 8) + 12 * 8 = 15 * 8
>   ZO = z_depth = 1
>
>   => hz_height = (15 * 8 / 2) * 1 = 60
>
> This particular case would probably fine as there is only one layer and still
> a lot of extra. But that may not be the case with higher odd layer numbers
> anymore.
>
> I would change this into:
>
>          hz_height = ALIGN(qpitch * Z0 / 2, vertical_align);

The comment above the assignment is from the docs, and it uses the
constant 8, rather than 'j', so I thought it would be better just to
use 8. Although, you are right that it is probably 8 because they set
'j' as 8 for the purposes of hiz calculations.

I also wanted to do the ALIGN before the integer / 2.

How do you feel about:
hz_height = ALIGN(qpitch * Z0, 8) / 2;

I also think this alternative is closest to the docs:
hz_height = CEILING(qpitch * Z0, 2 * 8) * 8;

-Jordan