[ET-VK] Use performant tiled algorithm for 4 bit weight only quantized linear

## Context

As title. Update the default compute shader for weight-only quantized int4 linear to use a tiled algorithm, which should boost performance for `gemm` cases, i.e. where `mat1` is a matrix.

## Changes

* Changed `q_4w_linear` name to `q_4w_linear_tiled` name
* Update the compute shader to use tiled algorithm

Using a value of 3 for `TILE_ROWS`; I expect to add variants which switch between different output tile configurations.

Differential Revision: [D73044649](https://our.internmc.facebook.com/intern/diff/D73044649/)

[ghstack-poisoned]

Author: SS-JIA

backends/vulkan/runtime/graph/ops/glsl/q_4w_linear.glsl renamed to backends/vulkan/runtime/graph/ops/glsl/q_4w_linear_tiled.glsl

@@ -13,10 +13,14 @@
 #define T ${buffer_scalar_type(DTYPE)}
 #define VEC4_T ${buffer_gvec_type(DTYPE, 4)}
 
+#define TILE_ROWS ${TILE_ROWS}
+
 ${define_required_extensions(DTYPE)}
 $if WEIGHT_STORAGE == "buffer":
   ${define_required_extensions("uint8")}
 
+#extension GL_EXT_control_flow_attributes : require
+
 layout(std430) buffer;
 
 ${layout_declare_tensor(B, "w", "t_out", DTYPE, OUT_STORAGE, is_scalar_array=False)}
@@ -53,10 +57,12 @@ layout(constant_id = 3) const int group_size = 64;
  *     first value contains the scale for the group and the second value
  *     contains the zero point for the group.
  *
+ * Each thread computes a tile of TILE_ROWS * 2 texels of the output tensor.
+ *
  * Note that this shader assumes that all tensors are width packed.
  */
 void main() {
-  const uint out_row = gl_GlobalInvocationID.y;
+  const uint out_row = gl_GlobalInvocationID.y * TILE_ROWS;
   // Each thread writes out 2 texels along the width axis, equivalent to 8
   // scalar elements. Therefore multiply the thread_idx.x by 8.
   const uint out_col = gl_GlobalInvocationID.x << 3;
@@ -70,10 +76,14 @@ void main() {
 
   const int num_blocks = mat1_sizes.x / group_size;
 
-  VEC4_T sums[2];
+  VEC4_T mat1[TILE_ROWS];
+  VEC4_T qmat2[4][2];
+  VEC4_T sums[TILE_ROWS][2];
 
-  sums[0] = VEC4_T(0);
-  sums[1] = VEC4_T(0);
+  [[unroll]] for (int r = 0; r < TILE_ROWS; ++r) {
+    sums[r][0] = VEC4_T(0);
+    sums[r][1] = VEC4_T(0);
+  }
 
   VEC4_T scales[2];
   VEC4_T zeros[2];
@@ -101,33 +111,51 @@ void main() {
     for (int g_idx = 0; g_idx < group_size; g_idx += 4) {
       const int k = block_idx * group_size + g_idx;
 
-      $if IN_STORAGE == "buffer":
-        const VEC4_T mat1_tex = t_mat1[(out_row * mat1_sizes.x + k) >> 2];
-      $else:
-        const VEC4_T mat1_tex = texelFetch(t_mat1, ivec3(k >> 2, out_row, 0), 0);
-
-      for (int comp = 0; comp < 4; ++comp) {
+      // Preload B
+      [[unroll]] for (int r = 0; r < 4; ++r) {
         $if WEIGHT_STORAGE == "buffer":
-          const u8vec4 packed_weight_tex = t_qmat2[(k + comp) * qmat2_stride + gl_GlobalInvocationID.x];
+          const u8vec4 packed_weight_tex = t_qmat2[(k + r) * qmat2_stride + gl_GlobalInvocationID.x];
         $else:
           const uvec4 packed_weight_tex = texelFetch(
               t_qmat2,
-              ivec2(gl_GlobalInvocationID.x, k + comp),
+              ivec2(gl_GlobalInvocationID.x, k + r),
               0);
 
-        const uvec4 weight_tex_1 = (packed_weight_tex & 0xF0) >> 4;
-        const uvec4 weight_tex_2 = packed_weight_tex & 0x0F;
+        qmat2[r][0] = (VEC4_T((packed_weight_tex & 0xF0) >> 4) - 8.0) * scales[0] + zeros[0];
+        qmat2[r][1] = (VEC4_T(packed_weight_tex & 0x0F) - 8.0) * scales[1] + zeros[1];
+      }
+
+      // Preload A
+      [[unroll]] for (int r = 0; r < TILE_ROWS; ++r) {
+        $if IN_STORAGE == "buffer":
+          mat1[r] = t_mat1[((out_row + r) * mat1_sizes.x + k) >> 2];
+        $else:
+          mat1[r] = texelFetch(t_mat1, ivec3(k >> 2, out_row + r, 0), 0);
+      }
 
-        sums[0] += mat1_tex[comp] * ((vec4(weight_tex_1) - 8.0) * scales[0] + zeros[0]);
-        sums[1] += mat1_tex[comp] * ((vec4(weight_tex_2) - 8.0) * scales[1] + zeros[1]);
+      // Accumulate output tile
+      [[unroll]] for (int r = 0; r < TILE_ROWS; ++r) {
+        sums[r][0] +=   mat1[r].x * qmat2[0][0]
+                      + mat1[r].y * qmat2[1][0]
+                      + mat1[r].z * qmat2[2][0]
+                      + mat1[r].w * qmat2[3][0];
+
+        sums[r][1] +=   mat1[r].x * qmat2[0][1]
+                      + mat1[r].y * qmat2[1][1]
+                      + mat1[r].z * qmat2[2][1]
+                      + mat1[r].w * qmat2[3][1];
       }
     }
   }
 
-  $if OUT_STORAGE == "buffer":
-    t_out[(out_row * out_sizes.x + out_col) >> 2] = sums[0];
-    t_out[(out_row * out_sizes.x + out_col + 4) >> 2] = sums[1];
-  $else:
-    imageStore(t_out, ivec3(out_col_texel_idx, out_row, 0), sums[0]);
-    imageStore(t_out, ivec3(out_col_texel_idx + 1, out_row, 0), sums[1]);
+  [[unroll]] for (int r = 0; r < TILE_ROWS; ++r) {
+    $if OUT_STORAGE == "buffer":
+      if (out_row + r < out_sizes.y) {
+        t_out[((out_row + r) * out_sizes.x + out_col) >> 2] = sums[r][0];
+        t_out[((out_row + r) * out_sizes.x + out_col + 4) >> 2] = sums[r][1];
+      }
+    $else:
+      imageStore(t_out, ivec3(out_col_texel_idx, out_row + r, 0), sums[r][0]);
+      imageStore(t_out, ivec3(out_col_texel_idx + 1, out_row + r, 0), sums[r][1]);
+  }
 }

backends/vulkan/runtime/graph/ops/glsl/q_4w_linear.yaml renamed to backends/vulkan/runtime/graph/ops/glsl/q_4w_linear_tiled.yaml

@@ -4,19 +4,20 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
-q_4w_linear:
+q_4w_linear_tiled:
   parameter_names_with_default_values:
     DTYPE: float
     OUT_STORAGE: texture3d
     IN_STORAGE: texture3d
     WEIGHT_STORAGE: texture2d
     PARAMS_STORAGE: buffer
+    TILE_ROWS: 3
   shader_variants:
-    - NAME: q_4w_linear_texture3d_texture3d_texture2d_float
-    - NAME: q_4w_linear_buffer_buffer_texture2d_float
+    - NAME: q_4w_linear_tiled_texture3d_texture3d_texture2d_float
+    - NAME: q_4w_linear_tiled_buffer_buffer_texture2d_float
       OUT_STORAGE: buffer
       IN_STORAGE: buffer
-    - NAME: q_4w_linear_buffer_buffer_buffer_float
+    - NAME: q_4w_linear_tiled_buffer_buffer_buffer_float
       OUT_STORAGE: buffer
       IN_STORAGE: buffer
       WEIGHT_STORAGE: buffer

backends/vulkan/runtime/graph/ops/impl/QuantizedLinearGroupwiseInt4.cpp

@@ -146,6 +146,8 @@ void add_q_4w_linear_node(
   std::string kernel_name = "q_4w_linear";
   if (use_coop_algorithm) {
     kernel_name += "_coop";
+  } else {
+    kernel_name += "_tiled";
   }
   add_storage_type_suffix(kernel_name, graph.storage_type_of(out));
   add_storage_type_suffix(kernel_name, graph.storage_type_of(mat1));
@@ -154,10 +156,12 @@ void add_q_4w_linear_node(
 
   utils::uvec3 global_wg_size = graph.logical_limits_of(out);
   global_wg_size[0] = utils::div_up(global_wg_size[0], uint32_t(2));
-
   utils::uvec3 local_wg_size = graph.create_local_wg_size(global_wg_size);
+
   if (use_coop_algorithm) {
     local_wg_size = {8, 1, 8};
+  } else {
+    global_wg_size[1] = utils::div_up(global_wg_size[1], uint32_t(3));
   }
 
   graph.execute_nodes().emplace_back(new DispatchNode(