[Mesa-dev] [PATCH 23/23] i965/gen9: Enable lossless compression

[Topi Pohjolainen]

I tried first creating the auxiliary buffer the same time with the
color buffer. That, however, led me into a situation where we would
later create the rest of the mip-levels and the compression would
need to be disabled (it is only supported for single level buffers).

Here we try to create it on demand just before the hardware starts
to render. This is similar what we do with fast clear buffers,
their creation is deferred until the first clear.
This setup also gives the opportunity to detect if the miptree
represents the temporaty texture used internally in the mesa core.
This texture is mostly written by cpu and therefore enabling
compression for it doesn't make much sense.

Note that a heuristic is included. Floating point formats are not
enabled yet as they are only seen to hurt performance.

Some highlights with window system driver kept fixed to default
and only the application driver changing:

Manhattan: 8.32152% +/- 0.355881%
Offscreen: 9.09713% +/- 0.340763%

Glb trex: 8.46231% +/- 0.460624%
Offscreen: 9.31872% +/- 0.463743%

Numbers from our system where the driver is changed also for
the windowing environment:

GFXBench3_Manhattan             41.8 FPS  12.0 %  46.8 FPS
GFXBench3_Manhattan_OffScreen   48.7 FPS  9.0 %   53.1 FPS

GLBenchmark_Trex_FixedTime            133.0 FPS  9.0 %   145.0 FPS
GLBenchmark_Trex_FixedTime_OffScreen  168.0 FPS  9.5 %   184.0 FPS

Unigine-heaven regresses: -2.31021% +/- 0.217207%. There are no color
resolves needed during the run so the hit comes from something else.
Perhaps the content is such that it doesn't really compress but
the additional work required of the hardware to maintain the
associated meta data slows us down.

Signed-off-by: Topi Pohjolainen <topi.pohjolainen at intel.com>
---
 src/mesa/drivers/dri/i965/gen8_surface_state.c |  9 +++++++++
 src/mesa/drivers/dri/i965/intel_mipmap_tree.c  | 23 ++++++++++++++++++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/gen8_surface_state.c b/src/mesa/drivers/dri/i965/gen8_surface_state.c
index eaf5874..b9b6b5a 100644
--- a/src/mesa/drivers/dri/i965/gen8_surface_state.c
+++ b/src/mesa/drivers/dri/i965/gen8_surface_state.c
@@ -485,6 +485,15 @@ gen8_update_renderbuffer_surface(struct brw_context *brw,
                        __func__, _mesa_get_format_name(rb_format));
    }
 
+   /* Consider if lossless compression is supported but the needed
+    * auxiliary buffer doesn't exist yet.
+    */
+   if (brw->gen >= 9 && mt->mcs_mt == NULL &&
+       intel_tiling_supports_non_msrt_mcs(brw, mt->tiling) &&
+       intel_miptree_supports_non_msrt_fast_clear(brw, mt) &&
+       intel_miptree_supports_lossless_compressed(mt->format))
+      intel_miptree_alloc_non_msrt_mcs(brw, mt);
+
    struct intel_mipmap_tree *aux_mt = mt->mcs_mt;
    const uint32_t aux_mode = gen8_get_aux_mode(brw, mt, surf_type);
 
diff --git a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
index 59961f2..083139a 100644
--- a/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
+++ b/src/mesa/drivers/dri/i965/intel_mipmap_tree.c
@@ -770,7 +770,8 @@ intel_miptree_create(struct brw_context *brw,
    /* If this miptree is capable of supporting fast color clears, set
     * fast_clear_state appropriately to ensure that fast clears will occur.
     * Allocation of the MCS miptree will be deferred until the first fast
-    * clear actually occurs.
+    * clear actually occurs or when compressed single sampled buffer is
+    * written by the GPU for the first time.
     */
    if (intel_tiling_supports_non_msrt_mcs(brw, mt->tiling) &&
        intel_miptree_supports_non_msrt_fast_clear(brw, mt)) {
@@ -1598,6 +1599,26 @@ intel_miptree_alloc_non_msrt_mcs(struct brw_context *brw,
                                INTEL_MSAA_LAYOUT_NONE,
                                layout_flags);
 
+   /* From Gen9 onwards single-sampled (non-msrt) auxiliary buffers are
+    * used for lossless compression which requires similar initialisation
+    * as multi-sample compression.
+    */
+   if (brw->gen >= 9 &&
+       intel_miptree_supports_lossless_compressed(mt->format)) {
+      /* Hardware sets the auxiliary buffer to all zeroes when it does full
+       * resolve. Initialize it accordingly in case the first renderer is
+       * cpu (or other none compression aware party).
+       *
+       * This is also explicitly stated in the spec (MCS Buffer for Render
+       * Target(s)):
+       *   "If Software wants to enable Color Compression without Fast clear,
+       *    Software needs to initialize MCS with zeros."
+       */
+      intel_miptree_init_mcs(brw, mt, 0);
+      mt->fast_clear_state = INTEL_FAST_CLEAR_STATE_RESOLVED;
+      mt->msaa_layout = INTEL_MSAA_LAYOUT_CSS;
+   }
+
    return mt->mcs_mt;
 }
 
-- 
2.5.0