Add groups to 2-D convolutions (#1129)

* Added groups to 2-D convolutions. Only implemented for **some** specializations.

Also fixed 1D grouped convs with different kernel strides and added more tests.

* fix channels condition

mlx/backend/metal/conv.cpp

@@ -257,15 +257,19 @@ void implicit_gemm_conv_2D_gpu(
     const array& wt,
     array out,
     const MLXConvParams<2>& conv_params) {
+  const int groups = conv_params.groups;
+  const int C_per_group = conv_params.C / conv_params.groups;
+  const int O_per_group = conv_params.O / conv_params.groups;
+
   // Deduce implicit gemm size
-  int implicit_M = conv_params.N * conv_params.oS[0] * conv_params.oS[1];
-  int implicit_N = conv_params.O;
-  int implicit_K = conv_params.wS[0] * conv_params.wS[1] * conv_params.C;
+  const int implicit_M = conv_params.N * conv_params.oS[0] * conv_params.oS[1];
+  const int implicit_N = O_per_group;
+  const int implicit_K = conv_params.wS[0] * conv_params.wS[1] * C_per_group;
 
   // Determine block and warp tiles
   int wm = 2, wn = 2;
 
-  int bm = implicit_M >= 8192 && conv_params.C >= 64 ? 64 : 32;
+  int bm = implicit_M >= 8192 && C_per_group >= 64 ? 64 : 32;
   int bn = (bm == 64 || implicit_N >= 64) ? 64 : 32;
   int bk = 16;
 
@@ -281,15 +285,15 @@ void implicit_gemm_conv_2D_gpu(
 
   // Fix small channel specialization
   int n_channel_specialization = 0;
-  int channel_k_iters = ((conv_params.C + bk - 1) / bk);
+  int channel_k_iters = ((C_per_group + bk - 1) / bk);
   int gemm_k_iters = conv_params.wS[0] * conv_params.wS[1] * channel_k_iters;
 
-  if (conv_params.C <= 2) {
+  if (C_per_group <= 2) {
     gemm_k_iters = (implicit_K + bk - 1) / bk;
-    n_channel_specialization = conv_params.C;
-  } else if (conv_params.C <= 4) {
+    n_channel_specialization = C_per_group;
+  } else if (C_per_group <= 4) {
     gemm_k_iters = ((conv_params.wS[0] * conv_params.wS[1] * 4) + bk - 1) / bk;
-    n_channel_specialization = conv_params.C;
+    n_channel_specialization = C_per_group;
   }
 
   bool small_filter = (!n_channel_specialization) &&
@@ -340,7 +344,7 @@ void implicit_gemm_conv_2D_gpu(
   size_t grid_dim_x = tn * tile;
 
   MTL::Size group_dims = MTL::Size(32, wn, wm);
-  MTL::Size grid_dims = MTL::Size(grid_dim_x, grid_dim_y, 1);
+  MTL::Size grid_dims = MTL::Size(grid_dim_x, grid_dim_y, groups);
 
   // Encode arrays
   compute_encoder.set_input_array(in, 0);
@@ -703,6 +707,7 @@ void conv_2D_gpu(
     const std::vector<int>& wt_strides,
     const std::vector<int>& wt_dilation,
     const std::vector<int>& in_dilation,
+    const int groups,
     bool flip,
     std::vector<array>& copies) {
   // Make conv params
@@ -718,12 +723,12 @@ void conv_2D_gpu(
       /* const int kdil[NDIM] = */ {wt_dilation[0], wt_dilation[1]},
       /* const int idil[NDIM] = */ {in_dilation[0], in_dilation[1]},
       /* const size_t in_strides[NDIM + 2] = */
-      {in.strides()[0], in.strides()[1], in.strides()[2], in.strides()[3]},
+      {in.strides(0), in.strides(1), in.strides(2), in.strides(3)},
       /* const size_t wt_strides[NDIM + 2] = */
-      {wt.strides()[0], wt.strides()[1], wt.strides()[2], wt.strides()[3]},
+      {wt.strides(0), wt.strides(1), wt.strides(2), wt.strides(3)},
       /* const size_t out_strides[NDIM + 2] = */
-      {out.strides()[0], out.strides()[1], out.strides()[2], out.strides()[3]},
-      /* const int groups = */ 1,
+      {out.strides(0), out.strides(1), out.strides(2), out.strides(3)},
+      /* const int groups = */ groups,
       /* const bool flip = */ flip,
   };
 
@@ -735,6 +740,18 @@ void conv_2D_gpu(
   bool channels_large = (conv_params.C + conv_params.O) >= 512;
   bool channels_med = (conv_params.C + conv_params.O) >= 256;
 
+  if (groups > 1) {
+    const int C_per_group = conv_params.C / groups;
+    const int O_per_group = conv_params.O / groups;
+
+    if (is_idil_one && (C_per_group <= 4 || C_per_group % 16 == 0) &&
+        (O_per_group <= 16 || O_per_group % 16 == 0)) {
+      return implicit_gemm_conv_2D_gpu(s, d, in, wt, out, conv_params);
+    } else {
+      return explicit_gemm_conv_group_ND_gpu(s, d, in, wt, out, conv_params);
+    }
+  }
+
   // Direct to winograd conv
   if (!flip && is_stride_one && is_kdil_one && is_idil_one &&
       conv_params.wS[0] == 3 && conv_params.wS[1] == 3 &&
@@ -860,6 +877,7 @@ void Convolution::eval_gpu(const std::vector<array>& inputs, array& out) {
         kernel_strides_,
         kernel_dilation_,
         input_dilation_,
+        groups_,
         flip_,
         copies);
   }

mlx/backend/metal/kernels/conv.metal

@@ -109,6 +109,7 @@ template <typename T, int N>
   bool valid = n < params->N;
 
   // Unroll dimensions
+  int kernel_stride = 1;
   for (int i = N - 1; i >= 0; --i) {
     int os_ = (oS % params->oS[i]);
     int ws_ = (wS % params->wS[i]);
@@ -125,7 +126,8 @@ template <typename T, int N>
     oS /= params->oS[i];
     wS /= params->wS[i];
 
-    out += ws_ * params->str[i];
+    out += ws_ * kernel_stride;
+    kernel_stride *= params->wS[i];
   }
 
   if (valid) {

mlx/backend/metal/kernels/steel/conv/kernels/steel_conv.metal

@@ -133,9 +133,15 @@ implicit_gemm_conv_2d(
   const int c_col = tid_x * BN;
   const int K = gemm_params->K;
   const int N = gemm_params->N;
+  const int C_per_group = params->C / params->groups;
+
+  // Groups
+  A += tid.z * C_per_group;
+  B += tid.z * N * K;
+  C += tid.z * N;
 
   B += c_col * K;
-  C += c_row * N + c_col;
+  C += c_row * (N * params->groups) + c_col;
 
   const int2 offsets_a(0, c_row);
   const int2 offsets_b(0, c_col);
@@ -171,7 +177,8 @@ implicit_gemm_conv_2d(
   // Store results to device memory
   short tgp_bm = min(BM, gemm_params->M - c_row);
   short tgp_bn = min(BN, gemm_params->N - c_col);
-  mma_op.store_result_safe(C, N, short2(tgp_bn, tgp_bm));
+  const int ldc = N * params->groups;
+  mma_op.store_result_safe(C, ldc, short2(tgp_bn, tgp_bm));
 }
 
 #define instantiate_implicit_conv_2d(                                          \