[Mesa-dev] [PATCH v2] i965/blorp: Special-case the clear color in MSAA resolves

Jason Ekstrand jason at jlekstrand.net
Fri May 13 17:49:50 UTC 2016


On Wed, May 11, 2016 at 7:42 PM, Jason Ekstrand <jason at jlekstrand.net>
wrote:

> The current MSAA resolve code has a special-case for if the MCS value is 0.
> In this case we can only sample once because we know that all values are in
> slice 0.  This commit adds a second optimization that detecs the magic MCS
> value that indicates the clear color and grabs the color from a push
> constant and avoids sampling altogether.  On a microbenchmark written by
> Neil Roberts that tests resolving surfaces with just clear color, this
> improves performance by 60% for 8x, 40% for 4x, and 28% for 2x MSAA on my
> SKL gte3 laptop.  The benchmark can be found on the ML archive:
>
> https://lists.freedesktop.org/archives/mesa-dev/2016-February/108077.html
> ---
>  src/mesa/drivers/dri/i965/brw_blorp.h        |   4 +-
>  src/mesa/drivers/dri/i965/brw_blorp_blit.cpp | 101
> +++++++++++++++++++++++++--
>  2 files changed, 100 insertions(+), 5 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_blorp.h
> b/src/mesa/drivers/dri/i965/brw_blorp.h
> index 15114d0..9d71ca4 100644
> --- a/src/mesa/drivers/dri/i965/brw_blorp.h
> +++ b/src/mesa/drivers/dri/i965/brw_blorp.h
> @@ -197,7 +197,9 @@ struct brw_blorp_wm_push_constants
>     uint32_t src_z;
>
>     /* Pad out to an integral number of registers */
> -   uint32_t pad[5];
> +   uint32_t pad;
> +
> +   union gl_color_union clear_color;
>  };
>
>  #define BRW_BLORP_NUM_PUSH_CONSTANT_DWORDS \
> diff --git a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
> b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
> index 514a316..45b696d 100644
> --- a/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_blorp_blit.cpp
> @@ -346,6 +346,7 @@ struct brw_blorp_blit_vars {
>        nir_variable *offset;
>     } u_x_transform, u_y_transform;
>     nir_variable *u_src_z;
> +   nir_variable *u_clear_color;
>
>     /* gl_FragCoord */
>     nir_variable *frag_coord;
> @@ -374,6 +375,7 @@ brw_blorp_blit_vars_init(nir_builder *b, struct
> brw_blorp_blit_vars *v,
>     LOAD_UNIFORM(y_transform.multiplier, glsl_float_type())
>     LOAD_UNIFORM(y_transform.offset, glsl_float_type())
>     LOAD_UNIFORM(src_z, glsl_uint_type())
> +   LOAD_UNIFORM(clear_color, glsl_vec4_type())
>
>  #undef DECL_UNIFORM
>
> @@ -858,7 +860,8 @@ static nir_ssa_def *
>  blorp_nir_manual_blend_average(nir_builder *b, nir_ssa_def *pos,
>                                 unsigned tex_samples,
>                                 enum intel_msaa_layout tex_layout,
> -                               enum brw_reg_type dst_type)
> +                               enum brw_reg_type dst_type,
> +                               struct brw_blorp_blit_vars *v)
>  {
>     /* If non-null, this is the outer-most if statement */
>     nir_if *outer_if = NULL;
> @@ -867,9 +870,53 @@ blorp_nir_manual_blend_average(nir_builder *b,
> nir_ssa_def *pos,
>        nir_local_variable_create(b->impl, glsl_vec4_type(), "color");
>
>     nir_ssa_def *mcs = NULL;
> -   if (tex_layout == INTEL_MSAA_LAYOUT_CMS)
> +   if (tex_layout == INTEL_MSAA_LAYOUT_CMS) {
>        mcs = blorp_nir_txf_ms_mcs(b, pos);
>
> +      /* The MCS buffer stores a packed value that provides a mapping from
> +       * samples to array slices.  The magic value of all ones means that
> all
> +       * samples have the clear color.  In this case, we can
> short-circuit the
> +       * sampling process and just use the clear color that we pushed
> into the
> +       * shader.
> +       */
> +      nir_ssa_def *is_clear_color;
> +      switch (tex_samples) {
> +      case 2:
> +         /* Empirical evidence suggests that the value returned from the
> +          * sampler is not always 0x3 for clear color so we need to mask
> it.
> +          */
> +         is_clear_color =
> +            nir_ieq(b, nir_iand(b, nir_channel(b, mcs, 0), nir_imm_int(b,
> 0x3)),
> +                       nir_imm_int(b, 0x3));
> +         break;
> +      case 4:
> +         is_clear_color =
> +            nir_ieq(b, nir_channel(b, mcs, 0), nir_imm_int(b, 0xff));
> +         break;
> +      case 8:
> +         is_clear_color =
> +            nir_ieq(b, nir_channel(b, mcs, 0), nir_imm_int(b, ~0));
> +         break;
> +      case 16:
> +         is_clear_color =
> +            nir_ior(b, nir_ieq(b, nir_channel(b, mcs, 0), nir_imm_int(b,
> ~0)),
>

This needs to be nir_iand.  Fixed locally...


> +                       nir_ieq(b, nir_channel(b, mcs, 1), nir_imm_int(b,
> ~0)));
> +         break;
> +      default:
> +         unreachable("Invalid sample count");
> +      }
> +
> +      nir_if *if_stmt = nir_if_create(b->shader);
> +      if_stmt->condition = nir_src_for_ssa(is_clear_color);
> +      nir_cf_node_insert(b->cursor, &if_stmt->cf_node);
> +
> +      b->cursor = nir_after_cf_list(&if_stmt->then_list);
> +      nir_store_var(b, color, nir_load_var(b, v->u_clear_color), 0xf);
> +
> +      b->cursor = nir_after_cf_list(&if_stmt->else_list);
> +      outer_if = if_stmt;
> +   }
> +
>     /* We add together samples using a binary tree structure, e.g. for 4x
> MSAA:
>      *
>      *   result = ((sample[0] + sample[1]) + (sample[2] + sample[3])) / 4
> @@ -937,7 +984,8 @@ blorp_nir_manual_blend_average(nir_builder *b,
> nir_ssa_def *pos,
>           nir_store_var(b, color, texture_data[0], 0xf);
>
>           b->cursor = nir_after_cf_list(&if_stmt->else_list);
> -         outer_if = if_stmt;
> +         if (!outer_if)
> +            outer_if = if_stmt;
>        }
>
>        for (int j = 0; j < count_trailing_one_bits(i); j++) {
> @@ -1341,7 +1389,7 @@ brw_blorp_build_nir_shader(struct brw_context *brw,
>           /* Gen7+ hardware doesn't automaticaly blend. */
>           color = blorp_nir_manual_blend_average(&b, src_pos,
> key->src_samples,
>                                                  key->src_layout,
> -                                                key->texture_data_type);
> +                                                key->texture_data_type,
> &v);
>        }
>     } else if (key->blend && key->blit_scaled) {
>        color = blorp_nir_manual_blend_bilinear(&b, src_pos,
> key->src_samples, key, &v);
> @@ -1493,6 +1541,48 @@ compute_msaa_layout_for_pipeline(struct brw_context
> *brw, unsigned num_samples,
>  }
>
>
> +static union gl_color_union
> +brw_blorp_get_clear_color_for_mt(struct brw_context *brw,
> +                                 struct intel_mipmap_tree *mt,
> +                                 unsigned swizzle)
> +{
> +   union gl_color_union color;
> +   if (brw->gen >= 9) {
> +      color = mt->gen9_fast_clear_color;
> +   } else if (_mesa_is_format_integer(mt->format)) {
> +      color.i[0] = (mt->fast_clear_color_value & (1 << 31)) != 0;
> +      color.i[1] = (mt->fast_clear_color_value & (1 << 30)) != 0;
> +      color.i[2] = (mt->fast_clear_color_value & (1 << 29)) != 0;
> +      color.i[3] = (mt->fast_clear_color_value & (1 << 28)) != 0;
> +   } else {
> +      color.f[0] = (mt->fast_clear_color_value & (1 << 31)) != 0;
> +      color.f[1] = (mt->fast_clear_color_value & (1 << 30)) != 0;
> +      color.f[2] = (mt->fast_clear_color_value & (1 << 29)) != 0;
> +      color.f[3] = (mt->fast_clear_color_value & (1 << 28)) != 0;
> +   }
> +
> +   if (swizzle != SWIZZLE_NOOP) {
> +      union gl_color_union orig_color = color;
> +      for (unsigned i = 0; i < 4; i++) {
> +         unsigned s = GET_SWZ(swizzle, i);
> +         if (s <= SWIZZLE_W) {
> +            color.i[i] = orig_color.i[s];
> +         } else if (s == SWIZZLE_ZERO) {
> +            color.i[i] = 0;
> +         } else {
> +            assert(s == SWIZZLE_ONE);
> +            if (_mesa_is_format_integer(mt->format))
> +               color.i[i] = 1;
> +            else
> +               color.f[i] = 1;
> +         }
> +      }
> +   }
> +
> +   return color;
> +}
> +
> +
>  /**
>   * Note: if the src (or dst) is a 2D multisample array texture on Gen7+
> using
>   * INTEL_MSAA_LAYOUT_UMS or INTEL_MSAA_LAYOUT_CMS, src_layer (dst_layer)
> is
> @@ -1665,6 +1755,9 @@ brw_blorp_blit_miptrees(struct brw_context *brw,
>         params.src.num_samples <= 1 && params.dst.num_samples <= 1)
>        wm_prog_key.bilinear_filter = true;
>
> +   params.wm_push_consts.clear_color =
> +      brw_blorp_get_clear_color_for_mt(brw, src_mt, src_swizzle);
> +
>     GLenum base_format = _mesa_get_format_base_format(src_mt->format);
>     if (base_format != GL_DEPTH_COMPONENT && /* TODO: what about
> depth/stencil? */
>         base_format != GL_STENCIL_INDEX &&
> --
> 2.5.0.400.gff86faf
>
>
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