[ET-VK] Add co-op algorithm for 4 bit weight only quantized linear

## Context

As title. Add an alternative compute shader for int4 weight-only quantized linear that utilizes a co-operative algorithm. This shader is more performant than standard tiled algorithms for `gemv` cases, i.e. when `mat1` is a vector rather than a matrix.

## Changes

* Add the cooperative shader
* Use the cooperative shader when the height of `mat1` is 1

Differential Revision: [D73044650](https://our.internmc.facebook.com/intern/diff/D73044650/)

[ghstack-poisoned]

Author: SS-JIA

backends/vulkan/runtime/graph/ops/glsl/q_4w_linear_coop.glsl

@@ -0,0 +1,199 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#version 450 core
+
+#define PRECISION ${PRECISION}
+
+#define T ${buffer_scalar_type(DTYPE)}
+#define VEC4_T ${buffer_gvec_type(DTYPE, 4)}
+
+#define TILE_ROWS ${TILE_ROWS}
+
+#define NGROUPS 8
+#define NWORKERS 8
+
+${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)}
+${layout_declare_tensor(B, "r", "t_mat1", DTYPE, IN_STORAGE, is_scalar_array=False)}
+${layout_declare_tensor(B, "r", "t_qmat2", "uint8", WEIGHT_STORAGE, is_scalar_array=False)}
+${layout_declare_tensor(B, "r", "t_qparams", DTYPE, "buffer", is_scalar_array=False)}
+
+layout(push_constant) uniform restrict Block {
+  ivec4 out_sizes;
+  ivec4 mat1_sizes;
+  ivec4 qmat2_sizes;
+};
+
+layout(local_size_x_id = 0, local_size_y_id = 1, local_size_z_id = 2) in;
+
+layout(constant_id = 3) const int group_size = 64;
+
+shared VEC4_T partial_sums[NGROUPS][NWORKERS][TILE_ROWS][2];
+
+/*
+ * This shader computes a linear operator between a floating point input matrix
+ * x and a weights matrix that is quantized to 4 bits. Please refer to the
+ * q_4w_linear shader for more details.
+ *
+ * This shader implements a co-operative algorithm to compute the output. The
+ * work group size is {NGROUP, 1, NWORKERS}, and each group of NWORKERS threads
+ * cooperative to compute TILE_ROWS * 2 output texels. Therefore,
+ * NGROUP * TILE_ROWS * 2 output texels are computed across one work group.
+ *
+ * The threads co-operate by each thread computing a partial reduction along the
+ * K dimension. To illustrate the computation, consider a scalar variant of the
+ * algorithm that computes the dot product of 2 vectors. Also assume that
+ * NWORKERS is 8.
+ *
+ * Thread 1 in each group will compute:
+ * (mat1[0] * mat2[0]) + (mat1[8] * mat2[8]) + (mat1[16] * mat2[16]) + ...
+ *
+ * Thread 2 in each group will compute:
+ * (mat1[1] * mat2[1]) + (mat2[9] * mat2[9]) + (mat1[17] * mat2[17]) + ...
+ *
+ * Thread 3 in each group will compute:
+ * (mat1[2] * mat2[2]) + (mat2[10] * mat2[10]) + (mat1[18] * mat2[18]) + ...
+ *
+ * The partial accumulations is structured such that memory accesses in each
+ * loop iteration can be coalesced.
+ *
+ * Then, at the end first thread in each group will accumulate the partial
+ * accumulations computed by each thread to obtain the final result.
+ *
+ * Note that this shader assumes that all tensors are width packed.
+ */
+void main() {
+  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;
+  // Similar reasoning to the above, each thread works on 2 texels along the
+  // width axis so multiply thread_idx.x by 2.
+  const int out_col_texel_idx = int(gl_GlobalInvocationID.x) << 1;
+
+  const uint gid = gl_LocalInvocationID.x; // group id
+  const uint wid = gl_LocalInvocationID.z; // worker id
+
+  if (out_col >= out_sizes.x || out_row >= out_sizes.y) {
+    return;
+  }
+
+  const int num_blocks = mat1_sizes.x / group_size;
+
+  VEC4_T mat1[TILE_ROWS];
+  VEC4_T qmat2[4][2];
+  VEC4_T local_sums[TILE_ROWS][2];
+
+  [[unroll]] for (int r = 0; r < TILE_ROWS; ++r) {
+    local_sums[r][0] = VEC4_T(0);
+    local_sums[r][1] = VEC4_T(0);
+  }
+
+  VEC4_T scales[2];
+  VEC4_T zeros[2];
+
+  $if WEIGHT_STORAGE == "buffer":
+    const int qmat2_stride = qmat2_sizes.x >> 2;
+  $if PARAMS_STORAGE == "buffer":
+    const int qparams_y_stride = out_sizes.x >> 2;
+    const int qparams_z_stride = qparams_y_stride * 2;
+
+  for (int block_idx = 0; block_idx < num_blocks; ++block_idx) {
+    $if PARAMS_STORAGE == "buffer":
+      scales[0] = t_qparams[block_idx * qparams_z_stride + out_col_texel_idx];
+      zeros[0] = t_qparams[block_idx * qparams_z_stride + out_col_texel_idx + qparams_y_stride];
+
+      scales[1] = t_qparams[block_idx * qparams_z_stride + out_col_texel_idx + 1];
+      zeros[1] = t_qparams[block_idx * qparams_z_stride + out_col_texel_idx + 1 + qparams_y_stride];
+    $else:
+      scales[0] = texelFetch(t_qparams, ivec3(out_col_texel_idx, 0, block_idx), 0);
+      zeros[0] = texelFetch(t_qparams, ivec3(out_col_texel_idx, 1, block_idx), 0);
+
+      scales[1] = texelFetch(t_qparams, ivec3(out_col_texel_idx + 1, 0, block_idx), 0);
+      zeros[1] = texelFetch(t_qparams, ivec3(out_col_texel_idx + 1, 1, block_idx), 0);
+
+    for (uint g_idx = 4 * wid; g_idx < group_size; g_idx += (4 * NWORKERS)) {
+      const uint k = block_idx * group_size + g_idx;
+
+      // Preload B
+      [[unroll]] for (int r = 0; r < 4; ++r) {
+        $if WEIGHT_STORAGE == "buffer":
+          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 + r),
+              0);
+
+        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);
+      }
+
+      // Accumulate local output tile
+      [[unroll]] for (int r = 0; r < TILE_ROWS; ++r) {
+        local_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];
+
+        local_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];
+      }
+    }
+  }
+
+  [[unroll]] for (int r = 0; r < TILE_ROWS; ++r) {
+    partial_sums[gid][wid][r][0] = local_sums[r][0];
+    partial_sums[gid][wid][r][1] = local_sums[r][1];
+  }
+
+  memoryBarrierShared();
+  barrier();
+
+  if (wid != 0) {
+    return;
+  }
+
+  VEC4_T sums[TILE_ROWS][2];
+
+  for (int r = 0; r < TILE_ROWS; ++r) {
+    sums[r][0] = VEC4_T(0);
+    sums[r][1] = VEC4_T(0);
+    [[unroll]] for (int worker = 0; worker < NWORKERS; ++ worker) {
+      sums[r][0] += partial_sums[gid][worker][r][0];
+      sums[r][1] += partial_sums[gid][worker][r][1];
+    }
+  }
+
+  [[unroll]] for (int r = 0; r < TILE_ROWS; ++r) {
+    $if OUT_STORAGE == "buffer":
+      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_coop.yaml

@@ -0,0 +1,23 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# 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_coop:
+  parameter_names_with_default_values:
+    DTYPE: float
+    OUT_STORAGE: texture3d
+    IN_STORAGE: texture3d
+    WEIGHT_STORAGE: texture2d
+    PARAMS_STORAGE: buffer
+    TILE_ROWS: 1
+  shader_variants:
+    - NAME: q_4w_linear_coop_texture3d_texture3d_texture2d_float
+    - NAME: q_4w_linear_coop_buffer_buffer_texture2d_float
+      OUT_STORAGE: buffer
+      IN_STORAGE: buffer
+    - NAME: q_4w_linear_coop_buffer_buffer_buffer_float
+      OUT_STORAGE: buffer
+      IN_STORAGE: buffer
+      WEIGHT_STORAGE: buffer

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

@@ -128,24 +128,37 @@ void add_q_4w_linear_node(
   check_q_4w_linear_args(
       graph, mat1, mat2_data, group_size, scales_and_zeros_data, out);
 
+  const uint32_t group_size_val = graph.extract_scalar<uint32_t>(group_size);
+
+  bool use_coop_algorithm = false;
+  // Apply the coop algorithm for gemv cases, i.e. mat1 is a vector as opposed
+  // to a matrix.
+  if (graph.size_at<uint32_t>(-2, mat1) == 1) {
+    use_coop_algorithm = true;
+  }
+
   ValueRef mat2 =
       prepack_int4_linear_weight_transposed_interleaved(graph, mat2_data);
 
   ValueRef scales_and_zeros = prepack_standard_hw_transposed(
       graph, scales_and_zeros_data, utils::kBuffer, utils::kWidthPacked);
 
   std::string kernel_name = "q_4w_linear";
+  if (use_coop_algorithm) {
+    kernel_name += "_coop";
+  }
   add_storage_type_suffix(kernel_name, graph.storage_type_of(out));
   add_storage_type_suffix(kernel_name, graph.storage_type_of(mat1));
   add_storage_type_suffix(kernel_name, graph.storage_type_of(mat2));
   add_dtype_suffix(kernel_name, graph.dtype_of(out));
 
-  const uint32_t group_size_val = graph.extract_scalar<uint32_t>(group_size);
-
   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};
+  }
 
   graph.execute_nodes().emplace_back(new DispatchNode(
       graph,

backends/vulkan/test/op_tests/linear_weight_int4_test.cpp

@@ -273,10 +273,24 @@ TEST(VulkanInt4LinearTest, test_reference_impl) {
       /*N = */ 32);
 }
 
-TEST(VulkanInt4LinearTest, test_vulkan_impl) {
+TEST(VulkanInt4LinearTest, test_vulkan_impl_small_m) {
   test_vulkan_linear_int4(
       /*B = */ 1,
       /*M = */ 4,
       /*K = */ 128,
       /*N = */ 32);
+
+  test_vulkan_linear_int4(
+      /*B = */ 1,
+      /*M = */ 1,
+      /*K = */ 256,
+      /*N = */ 256);
+}
+
+TEST(VulkanInt4LinearTest, test_vulkan_impl_gemm) {
+  test_vulkan_linear_int4(
+      /*B = */ 1,
+      /*M = */ 256,
+      /*K = */ 256,
+      /*N = */ 256);
 }