svga: reduce unmapping/remapping of the default constant buffer

Previously, every time we put shader constants into the default constant
buffer we called u_upload_alloc(), which mapped the buffer, and
u_upload_unmap().  We had to unmap the buffer before calling
svga_buffer_handle() to get the winsys handle for the buffer.  But we
really only need to do that the first time we reference the const buffer.
Now we try to keep the upload manager's buffer mapped until we fill it or
flush the command buffer.

v2: add additional comment on the buffer unmapping code in
svga_context_flush(), per Charmaine.

Reviewed-by: Charmaine Lee <[email protected]>

3 files changed, 40 insertions, 6 deletions

diff --git a/src/gallium/drivers/svga/svga_context.c b/src/gallium/drivers/svga/svga_context.c
index 78fb558f408..f498e839aa2 100644
--- a/src/gallium/drivers/svga/svga_context.c
+++ b/src/gallium/drivers/svga/svga_context.c
@@ -248,6 +248,8 @@ struct pipe_context *svga_context_create(struct pipe_screen *screen,
    svga->state.hw_draw.num_vbuffers = 0;
    memset(svga->state.hw_draw.vbuffers, 0,
           sizeof(svga->state.hw_draw.vbuffers));
+   svga->state.hw_draw.const0_buffer = NULL;
+   svga->state.hw_draw.const0_handle = NULL;
 
    /* Create a no-operation blend state which we will bind whenever the
     * requested blend state is impossible (e.g. due to having an integer
@@ -307,6 +309,17 @@ void svga_context_flush( struct svga_context *svga,
 
    svga->curr.nr_fbs = 0;
 
+   /* Unmap the 0th/default constant buffer.  The u_upload_unmap() function
+    * will call pipe_context::transfer_flush_region() to indicate the
+    * region of the buffer which was modified (and needs to be uploaded).
+    */
+   if (svga->state.hw_draw.const0_handle) {
+      assert(svga->state.hw_draw.const0_buffer);
+      u_upload_unmap(svga->const0_upload);
+      pipe_resource_reference(&svga->state.hw_draw.const0_buffer, NULL);
+      svga->state.hw_draw.const0_handle = NULL;
+   }
+
    /* Ensure that texture dma uploads are processed
     * before submitting commands.
     */
diff --git a/src/gallium/drivers/svga/svga_context.h b/src/gallium/drivers/svga/svga_context.h
index a635ef1fc95..db80061f425 100644
--- a/src/gallium/drivers/svga/svga_context.h
+++ b/src/gallium/drivers/svga/svga_context.h
@@ -355,6 +355,13 @@ struct svga_hw_draw_state
    /** Bitmask of enabled constant buffers */
    unsigned enabled_constbufs[PIPE_SHADER_TYPES];
 
+   /**
+    * These are used to reduce the number of times we call u_upload_unmap()
+    * while updating the zero-th/default VGPU10 constant buffer.
+    */
+   struct pipe_resource *const0_buffer;
+   struct svga_winsys_surface *const0_handle;
+
    /** VGPU10 HW state (used to prevent emitting redundant state) */
    SVGA3dDepthStencilStateId depth_stencil_id;
    unsigned stencil_ref;
diff --git a/src/gallium/drivers/svga/svga_state_constants.c b/src/gallium/drivers/svga/svga_state_constants.c
index dc80edf0982..8d6b46a1cae 100644
--- a/src/gallium/drivers/svga/svga_state_constants.c
+++ b/src/gallium/drivers/svga/svga_state_constants.c
@@ -646,15 +646,29 @@ emit_constbuf_vgpu10(struct svga_context *svga, enum pipe_shader_type shader)
       assert(extra_offset + extra_size <= new_buf_size);
       memcpy((char *) dst_map + extra_offset, extras, extra_size);
    }
-   u_upload_unmap(svga->const0_upload);
 
-   /* Issue the SetSingleConstantBuffer command */
-   dst_handle = svga_buffer_handle(svga, dst_buffer);
-   if (!dst_handle) {
-      pipe_resource_reference(&dst_buffer, NULL);
-      return PIPE_ERROR_OUT_OF_MEMORY;
+   /* Get winsys handle for the constant buffer */
+   if (svga->state.hw_draw.const0_buffer == dst_buffer &&
+       svga->state.hw_draw.const0_handle) {
+      /* re-reference already mapped buffer */
+      dst_handle = svga->state.hw_draw.const0_handle;
+   }
+   else {
+      /* we must unmap the buffer before getting the winsys handle */
+      u_upload_unmap(svga->const0_upload);
+
+      dst_handle = svga_buffer_handle(svga, dst_buffer);
+      if (!dst_handle) {
+         pipe_resource_reference(&dst_buffer, NULL);
+         return PIPE_ERROR_OUT_OF_MEMORY;
+      }
+
+      /* save the buffer / handle for next time */
+      pipe_resource_reference(&svga->state.hw_draw.const0_buffer, dst_buffer);
+      svga->state.hw_draw.const0_handle = dst_handle;
    }
 
+   /* Issue the SetSingleConstantBuffer command */
    assert(new_buf_size % 16 == 0);
    ret = SVGA3D_vgpu10_SetSingleConstantBuffer(svga->swc,
                                                0, /* index */