[Mesa-dev] [PATCH] i965: Add GPU BLIT of texture image to PBO in Intel driver

[Jon Ashburn]

Add Intel driver hook for glGetTexImage to accelerate the case of reading
texture image into a PBO.  This case gets huge performance gains by using
GPU BLIT directly to PBO rather than GPU BLIT to temporary texture followed
by memcpy.

No regressions on Piglit tests  with Intel driver.
Performance gain (1280 x 800 FBO, Ivybridge):
glGetTexImage + glMapBufferRange  with patch 1.45 msec
glGetTexImage + glMapBufferRange without patch 4.68 msec
---
 src/mesa/drivers/dri/i965/intel_tex_image.c | 114 ++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/intel_tex_image.c b/src/mesa/drivers/dri/i965/intel_tex_image.c
index ee02e68..1d0d72d 100644
--- a/src/mesa/drivers/dri/i965/intel_tex_image.c
+++ b/src/mesa/drivers/dri/i965/intel_tex_image.c
@@ -15,6 +15,8 @@
 #include "main/teximage.h"
 #include "main/texstore.h"
 
+#include "drivers/common/meta.h"
+
 #include "intel_mipmap_tree.h"
 #include "intel_buffer_objects.h"
 #include "intel_batchbuffer.h"
@@ -415,10 +417,122 @@ intel_image_target_texture_2d(struct gl_context *ctx, GLenum target,
                                   image->tile_x, image->tile_y);
 }
 
+static bool
+IntelBlitTexToPbo(struct gl_context * ctx,
+                   GLenum format, GLenum type,
+                   GLvoid * pixels, struct gl_texture_image *texImage)
+{
+   struct intel_texture_image *intelImage = intel_texture_image(texImage);
+   struct brw_context *brw = brw_context(ctx);
+   const struct gl_pixelstore_attrib *pack = &(ctx->Pack);
+   struct intel_buffer_object *dst = intel_buffer_object(pack->BufferObj);
+   GLuint dst_offset;
+   drm_intel_bo *dst_buffer;
+   GLenum target = texImage->TexObject->Target;
+
+   DBG("%s\n", __FUNCTION__);
+
+   /*
+    * Check if we can use GPU blit to copy from the hardware texture
+    * format to the user's format/type.
+    * Note that GL's pixel transfer ops don't apply to glGetTexImage()
+    */
+
+   if (!_mesa_format_matches_format_and_type(
+           intelImage->mt->format, format, type, false) ||
+         (_mesa_is_format_compressed(texImage->TexFormat) &&
+          _mesa_get_format_datatype(texImage->TexFormat) == GL_UNSIGNED_NORMALIZED)) {
+      DBG("%s - bad format for blit to PBO\n", __FUNCTION__);
+      return false;
+   }
+
+   if (ctx->_ImageTransferState) {
+      DBG("%s - bad transfer state for blit to PBO\n", __FUNCTION__);
+      return false;
+   }
+
+   if (pack->SkipPixels  || pack->SkipRows) {
+      DBG("%s - bad skip params for blit to PBO\n", __FUNCTION__);
+      return false;
+   }
+
+   if (pack->SwapBytes || pack->LsbFirst) {
+      DBG("%s: bad packing params\n", __FUNCTION__);
+      return false;
+   }
+
+   if (target == GL_TEXTURE_1D_ARRAY || target == GL_TEXTURE_CUBE_MAP_ARRAY ||
+       target == GL_TEXTURE_2D_ARRAY) {
+      DBG("%s: no support for array textures\n", __FUNCTION__);
+      return false;
+   }
+
+   int dst_stride = _mesa_image_row_stride(pack, texImage->Width, format, type);
+   bool dst_flip = false;
+   /* Mesa flips the dst_stride for ctx->Pack.Invert, our mt must have a
+    * normal dst_stride.
+    */
+   struct gl_pixelstore_attrib uninverted_pack = *pack;
+   if (ctx->Pack.Invert) {
+      dst_stride = -dst_stride;
+      dst_flip = true;
+      uninverted_pack.Invert = false;
+   }
+   dst_offset = (GLintptr) pixels;
+   dst_offset += _mesa_image_offset(2, &uninverted_pack, texImage->Width,
+                                    texImage->Height, format, type, 0, 0, 0);
+   dst_buffer = intel_bufferobj_buffer(brw, dst, dst_offset,
+                                       texImage->Height * dst_stride);
+
+   struct intel_mipmap_tree *pbo_mt =
+            intel_miptree_create_for_bo(brw,
+                                        dst_buffer,
+                                        intelImage->mt->format,
+                                        dst_offset,
+                                        texImage->Width, texImage->Height,
+                                        dst_stride, I915_TILING_NONE);
+
+   if (!pbo_mt)
+      return false;
+
+   if (!intel_miptree_blit(brw,
+                           intelImage->mt, texImage->Level, texImage->Face,
+                           0, 0, false,
+                           pbo_mt, 0, 0,
+                           0, 0, dst_flip,
+                           texImage->Width, texImage->Height, GL_COPY))
+      return false;
+
+   intel_miptree_release(&pbo_mt);
+
+   DBG("%s - DONE\n", __FUNCTION__);
+
+   return true;
+}
+
+static void
+intel_get_tex_image(struct gl_context *ctx,
+                       GLenum format, GLenum type, GLvoid *pixels,
+                       struct gl_texture_image *texImage) {
+   struct brw_context *brw = brw_context(ctx);
+   DBG("%s\n", __FUNCTION__);
+
+   if (_mesa_is_bufferobj(ctx->Pack.BufferObj)) {
+      /* Using PBOs, so try the BLT based path. */
+      if (IntelBlitTexToPbo(ctx, format, type, pixels, texImage))
+         return;
+
+      perf_debug("%s: fallback to CPU mapping in PBO case\n", __FUNCTION__);
+   }
+
+   _mesa_meta_GetTexImage(ctx, format, type, pixels, texImage);
+}
+
 void
 intelInitTextureImageFuncs(struct dd_function_table *functions)
 {
    functions->TexImage = intelTexImage;
    functions->EGLImageTargetTexture2D = intel_image_target_texture_2d;
    functions->BindRenderbufferTexImage = intel_bind_renderbuffer_tex_image;
+   functions->GetTexImage = intel_get_tex_image;
 }
-- 
1.8.1.2