Improve runtime complexity of roi_align

Author: hvaara

torchvision/csrc/ops/mps/mps_kernels.h

@@ -225,105 +225,96 @@ kernel void nms<DTYPE ## 4, DTYPE>(                        \
   uint2    tgid   [[threadgroup_position_in_grid]],        \
   uint2    tid2   [[thread_position_in_threadgroup]]);
 
-template<typename T, typename integer_t>
+template <typename T, typename integer_t>
 kernel void roi_align(
     constant T       * input          [[buffer(0)]],
     constant T       * rois           [[buffer(1)]],
     device   T       * output         [[buffer(2)]],
-    constant int64_t & output_size    [[buffer(3)]],
+    constant float   & spatial_scale  [[buffer(3)]],
     constant int64_t & channels       [[buffer(4)]],
     constant int64_t & height         [[buffer(5)]],
     constant int64_t & width          [[buffer(6)]],
     constant int64_t & pooled_height  [[buffer(7)]],
     constant int64_t & pooled_width   [[buffer(8)]],
     constant int64_t & sampling_ratio [[buffer(9)]],
     constant bool    & aligned        [[buffer(10)]],
-    constant float   & spatial_scale  [[buffer(11)]],
-    uint2     tgid   [[threadgroup_position_in_grid]],
-    uint2     tptg   [[threads_per_threadgroup]],
-    uint2     tid2   [[thread_position_in_threadgroup]]){
-  MPS_1D_KERNEL_LOOP(index, output_size, 1) {
-    // (n, c, ph, pw) is an element in the pooled output
-    integer_t pw = index % pooled_width;
-    integer_t ph = (index / pooled_width) % pooled_height;
-    integer_t c = (index / pooled_width / pooled_height) % channels;
-    integer_t n = index / pooled_width / pooled_height / channels;
-
-    constant T* offset_rois = rois + n * 5;
-    integer_t roi_batch_ind = offset_rois[0];
-
-    // Do not using rounding; this implementation detail is critical
-    T offset = aligned ? (T)0.5 : (T)0.0;
-    T roi_start_w = offset_rois[1] * spatial_scale - offset;
-    T roi_start_h = offset_rois[2] * spatial_scale - offset;
-    T roi_end_w = offset_rois[3] * spatial_scale - offset;
-    T roi_end_h = offset_rois[4] * spatial_scale - offset;
-
-    T roi_width = roi_end_w - roi_start_w;
-    T roi_height = roi_end_h - roi_start_h;
-    if (!aligned) {
-      // Force malformed ROIs to be 1x1
-      roi_width = max(roi_width, (T)1.);
-      roi_height = max(roi_height, (T)1.);
-    }
-
-    T bin_size_h = static_cast<T>(roi_height) / static_cast<T>(pooled_height);
-    T bin_size_w = static_cast<T>(roi_width) / static_cast<T>(pooled_width);
-
-    constant T* offset_input =
-        input + (roi_batch_ind * channels + c) * height * width;
-
-    // We use roi_bin_grid to sample the grid and mimic integral
-    integer_t roi_bin_grid_h = (sampling_ratio > 0)
-        ? sampling_ratio
-        : ceil(roi_height / pooled_height); // e.g., = 2
-    integer_t roi_bin_grid_w =
-        (sampling_ratio > 0) ? sampling_ratio : ceil(roi_width / pooled_width);
-
-    // We do average (integral) pooling inside a bin
-    // When the grid is empty, output zeros.
-    const T count = max(roi_bin_grid_h * roi_bin_grid_w, static_cast<integer_t>(1)); // e.g. = 4
-
-    T output_val = 0.;
-    for (integer_t iy = 0; iy < roi_bin_grid_h; iy++) // e.g., iy = 0, 1
-    {
-      const T y = roi_start_h + ph * bin_size_h +
-          static_cast<T>(iy + .5f) * bin_size_h /
-              static_cast<T>(roi_bin_grid_h); // e.g., 0.5, 1.5
-      for (integer_t ix = 0; ix < roi_bin_grid_w; ix++) {
-        const T x = roi_start_w + pw * bin_size_w +
-            static_cast<T>(ix + .5f) * bin_size_w /
-                static_cast<T>(roi_bin_grid_w);
+    uint     index   [[thread_position_in_grid]])
+{
+  // Decode linear index into (n, c, ph, pw)
+  integer_t pw = index % pooled_width;
+  integer_t ph = (index / pooled_width) % pooled_height;
+  integer_t c = (index / pooled_width / pooled_height) % channels;
+  integer_t n = index / (pooled_width * pooled_height * channels);
+
+  constant T* offset_rois = rois + n * 5;
+  integer_t roi_batch_ind = static_cast<integer_t>(offset_rois[0]);
+
+  // Do not using rounding; this implementation detail is critical
+  T offset = aligned ? static_cast<T>(0.5) : static_cast<T>(0.0);
+  T roi_start_w = offset_rois[1] * spatial_scale - offset;
+  T roi_start_h = offset_rois[2] * spatial_scale - offset;
+  T roi_end_w   = offset_rois[3] * spatial_scale - offset;
+  T roi_end_h   = offset_rois[4] * spatial_scale - offset;
+
+  T roi_width = roi_end_w - roi_start_w;
+  T roi_height = roi_end_h - roi_start_h;
+
+  if (!aligned) {
+    // Force malformed ROIs to be 1x1
+    roi_width = max(roi_width, static_cast<T>(1.0));
+    roi_height = max(roi_height, static_cast<T>(1.0));
+  }
 
-        T val = bilinear_interpolate(offset_input, height, width, y, x, index);
-        output_val += val;
-      }
+  T bin_size_h = roi_height / static_cast<T>(pooled_height);
+  T bin_size_w = roi_width / static_cast<T>(pooled_width);
+
+  constant T* offset_input = input + (roi_batch_ind * channels + c) * height * width;
+
+  // We use roi_bin_grid to sample the grid and mimic integral
+  integer_t roi_bin_grid_h = sampling_ratio > 0
+    ? sampling_ratio
+    : static_cast<integer_t>(ceil(roi_height / static_cast<T>(pooled_height)));
+  integer_t roi_bin_grid_w = sampling_ratio > 0
+    ? sampling_ratio
+    : static_cast<integer_t>(ceil(roi_width / static_cast<T>(pooled_width)));
+
+  // We do average (integral) pooling inside a bin
+  // When the grid is empty, output zeros.
+  const T count = max(roi_bin_grid_h * roi_bin_grid_w, static_cast<integer_t>(1));
+  T output_val = static_cast<T>(0.0);
+
+  for (integer_t iy = 0; iy < roi_bin_grid_h; iy++) {
+    T y = roi_start_h + static_cast<T>(ph) * bin_size_h +
+          (static_cast<T>(iy) + static_cast<T>(0.5)) * bin_size_h / static_cast<T>(roi_bin_grid_h);
+    for (integer_t ix = 0; ix < roi_bin_grid_w; ix++) {
+      T x = roi_start_w + static_cast<T>(pw) * bin_size_w +
+            (static_cast<T>(ix) + static_cast<T>(0.5)) * bin_size_w / static_cast<T>(roi_bin_grid_w);
+
+      T val = bilinear_interpolate(offset_input, height, width, y, x, index);
+      output_val += val;
     }
-    output_val /= count;
-
-    output[index] = output_val;
   }
+
+  output_val /= count;
+  output[index] = output_val;
 }
 
-#define REGISTER_ROI_ALIGN_OP(DTYPE, INT_DTYPE)         \
-template                                                \
-[[host_name("roi_align_" #DTYPE)]]                      \
-kernel void roi_align<DTYPE, INT_DTYPE>(                \
-  constant DTYPE * input            [[buffer(0)]],      \
-  constant DTYPE * rois             [[buffer(1)]],      \
-  device   DTYPE * output           [[buffer(2)]],      \
-  constant int64_t & output_size    [[buffer(3)]],      \
-  constant int64_t & channels       [[buffer(4)]],      \
-  constant int64_t & height         [[buffer(5)]],      \
-  constant int64_t & width          [[buffer(6)]],      \
-  constant int64_t & pooled_height  [[buffer(7)]],      \
-  constant int64_t & pooled_width   [[buffer(8)]],      \
-  constant int64_t & sampling_ratio [[buffer(9)]],      \
-  constant bool    & aligned        [[buffer(10)]],     \
-  constant float   & spatial_scale  [[buffer(11)]],     \
-  uint2     tgid   [[threadgroup_position_in_grid]],    \
-  uint2     tptg   [[threads_per_threadgroup]],         \
-  uint2     tid2   [[thread_position_in_threadgroup]]);
+#define REGISTER_ROI_ALIGN_OP(DTYPE, INT_DTYPE)       \
+template                                              \
+[[host_name("roi_align_" #DTYPE)]]                    \
+kernel void roi_align<DTYPE, INT_DTYPE>(              \
+    constant DTYPE   * input          [[buffer(0)]],  \
+    constant DTYPE   * rois           [[buffer(1)]],  \
+    device   DTYPE   * output         [[buffer(2)]],  \
+    constant float   & spatial_scale  [[buffer(3)]],  \
+    constant int64_t & channels       [[buffer(4)]],  \
+    constant int64_t & height         [[buffer(5)]],  \
+    constant int64_t & width          [[buffer(6)]],  \
+    constant int64_t & pooled_height  [[buffer(7)]],  \
+    constant int64_t & pooled_width   [[buffer(8)]],  \
+    constant int64_t & sampling_ratio [[buffer(9)]],  \
+    constant bool    & aligned        [[buffer(10)]], \
+    uint     index   [[thread_position_in_grid]]);
 
 template<typename T, typename integer_t>
 kernel void roi_align_backward(
@@ -1005,7 +996,7 @@ kernel void ps_roi_pool_backward<DTYPE, INT_DTYPE>(          \
     constant int64_t & width           [[buffer(7)]],        \
     constant int64_t & pooled_height   [[buffer(8)]],        \
     constant int64_t & pooled_width    [[buffer(9)]],        \
-    constant int64_t & channels_out    [[buffer(10)]],       \ 
+    constant int64_t & channels_out    [[buffer(10)]],       \
     constant float   & spatial_scale   [[buffer(11)]],       \
     uint2     tgid   [[threadgroup_position_in_grid]],       \
     uint2     tptg   [[threads_per_threadgroup]],            \

torchvision/csrc/ops/mps/roi_align_kernel.mm

@@ -51,14 +51,14 @@
   dispatch_sync(mpsStream->queue(), ^() {
     @autoreleasepool {
       id<MTLComputeCommandEncoder> computeEncoder = mpsStream->commandEncoder();
-      MTLSize threadgroupsPerGrid = MTLSizeMake(
-          std::min(ceil_div(static_cast<int64_t>(output_size), static_cast<int64_t>(512)), static_cast<int64_t>(4096)),
-          1,
-          1);
 
       const std::string kernel = "roi_align_" + scalarToMetalTypeString(input.scalar_type());
       id<MTLComputePipelineState> visionPSO = mps::visionPipelineState(device, kernel);
 
+      auto threadsPerGrid = MTLSizeMake(output_size, 1, 1);
+      auto threadsPerThreadgroup =
+          MTLSizeMake(std::min(static_cast<int64_t>(visionPSO.maxTotalThreadsPerThreadgroup), output_size), 1, 1);
+
       // this function call is a no-op if MPS Profiler is not enabled
       getMPSProfiler().beginProfileKernel(visionPSO, kernel, {input_, rois_});
 
@@ -68,24 +68,16 @@
       [computeEncoder setBuffer:roisBuffer offset:rois_.storage_offset() * rois_.element_size() atIndex:1];
       [computeEncoder setBuffer:outputBuffer offset:output.storage_offset() * output.element_size() atIndex:2];
 
-      [computeEncoder setBytes:&output_size length:sizeof(int64_t) atIndex:3];
+      [computeEncoder setBytes:&spatial_scale_f length:sizeof(float) atIndex:3];
       [computeEncoder setBytes:&channels length:sizeof(int64_t) atIndex:4];
       [computeEncoder setBytes:&height length:sizeof(int64_t) atIndex:5];
       [computeEncoder setBytes:&width length:sizeof(int64_t) atIndex:6];
       [computeEncoder setBytes:&pooled_height length:sizeof(int64_t) atIndex:7];
       [computeEncoder setBytes:&pooled_width length:sizeof(int64_t) atIndex:8];
       [computeEncoder setBytes:&sampling_ratio length:sizeof(int64_t) atIndex:9];
       [computeEncoder setBytes:&aligned length:sizeof(bool) atIndex:10];
-      [computeEncoder setBytes:&spatial_scale_f length:sizeof(float) atIndex:11];
-
-      // A threadGroup is equivalent to a cuda's block.
-      NSUInteger tgSize = visionPSO.maxTotalThreadsPerThreadgroup;
-      if (tgSize > threadsPerBlock) {
-        tgSize = threadsPerBlock;
-      }
 
-      MTLSize threadGroupSize = MTLSizeMake(tgSize, 1, 1);
-      [computeEncoder dispatchThreadgroups:threadgroupsPerGrid threadsPerThreadgroup:threadGroupSize];
+      [computeEncoder dispatchThreads:threadsPerGrid threadsPerThreadgroup:threadsPerThreadgroup];
 
       getMPSProfiler().endProfileKernel(visionPSO);
     }