[ET-VK] Change weight packing in embedding

Pull Request resolved: #7063

The existing weight tensor for aten.embedding is created using a `tensor_like` from the output tensor, which defaults to channel packed.

However, the weight tensor is actually a 2D-tensor of `(num_embedding, dim_of_embedding)`. It is better in space to use either width or height packing.

This diff changes the implementation to use height-packing.
ghstack-source-id: 255439082

Differential Revision: [D66421366](https://our.internmc.facebook.com/intern/diff/D66421366/)

Author: yipjustin

backends/vulkan/runtime/graph/ops/glsl/embedding.glsl

@@ -47,9 +47,9 @@ void main() {
     const ivec3 in_lpos = ivec3(out_tidx.y, out_tidx.z * 4 + i, out_tidx.w / 4);
     const int in_texel_elem = load_texel_lpos(t_in, in_lpos, in_axis_map)[out_tidx.w % 4];
 
-    // Read weight tensor for embedding.
-    const ivec3 weight_lpos = ivec3(out_tidx.x, in_texel_elem, 0);
-    out_texel[i] = load_texel_lpos(t_weight, weight_lpos, weight_axis_map).x;
+    // Read weight tensor for embedding, it is height-packed.
+    const ivec3 weight_lpos = ivec3(out_tidx.x, in_texel_elem / 4, 0);
+    out_texel[i] = load_texel_lpos(t_weight, weight_lpos, weight_axis_map)[in_texel_elem % 4];
   }
 
   write_texel_lpos(t_out, out_lpos, out_texel, out_axis_map);

backends/vulkan/runtime/graph/ops/impl/Embedding.cpp

@@ -15,13 +15,21 @@
 
 #include <executorch/backends/vulkan/runtime/graph/ops/utils/ShaderNameUtils.h>
 
+#include <executorch/backends/vulkan/runtime/utils/StorageUtils.h>
+
 namespace vkcompute {
 
+using utils::GPUMemoryLayout;
+using utils::StorageType;
+
 void check_embedding_args(
     const api::vTensor& weight,
     const api::vTensor& in,
     const api::vTensor& out) {
-  VK_CHECK_COND(check_packed_dim_is(weight, WHCN::kChannelsDim));
+  // The packing logic may not be trivial here. Input and output are Channel
+  // Packed, which is default for the Vulkan backend. However, weight vector is
+  // height-packed instead of channel-packed for space reason.
+  VK_CHECK_COND(check_packed_dim_is(weight, WHCN::kHeightDim));
   VK_CHECK_COND(check_packed_dim_is(in, WHCN::kChannelsDim));
   VK_CHECK_COND(check_packed_dim_is(out, WHCN::kChannelsDim));
 }
@@ -58,7 +66,12 @@ void add_embedding_node(
 void embedding(ComputeGraph& graph, const std::vector<ValueRef>& args) {
   ValueRef in = args[1];
   ValueRef out = args[5];
-  ValueRef weight = prepack_standard_like(graph, args[0], out);
+
+  ValueRef weight = prepack_standard(
+      graph,
+      args[0],
+      StorageType::TEXTURE_2D,
+      GPUMemoryLayout::TENSOR_HEIGHT_PACKED);
 
   add_embedding_node(graph, weight, in, out);
 }