Add recursive work splitting to EvalShardedByInnerDimContext

unsupported/Eigen/CXX11/src/Tensor/TensorContractionThreadPool.h

@@ -1159,16 +1159,7 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
     template <int Alignment>
     void run() {
       Barrier barrier(internal::convert_index<int>(num_blocks));
-      for (Index block_idx = 0; block_idx < num_blocks; ++block_idx) {
+      eval<Alignment>(barrier, 0, num_blocks);
-        evaluator->m_device.enqueueNoNotification(
-            [this, block_idx, &barrier]() {
-              Index block_start = block_idx * block_size;
-              Index block_end = block_start + actualBlockSize(block_idx);
-
-              processBlock<Alignment>(block_idx, block_start, block_end);
-              barrier.Notify();
-            });
-      }
       barrier.Wait();
 
       // Aggregate partial sums from l0 ranges.
@@ -1180,38 +1171,7 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
 
     template <int Alignment>
     void runAsync() {
-      for (Index block_idx = 0; block_idx < num_blocks; ++block_idx) {
+      evalAsync<Alignment>(0, num_blocks);
-        evaluator->m_device.enqueueNoNotification([this, block_idx]() {
-          Index block_start = block_idx * block_size;
-          Index block_end = block_start + actualBlockSize(block_idx);
-
-          processBlock<Alignment>(block_idx, block_start, block_end);
-
-          int v = num_pending_blocks.fetch_sub(1);
-          eigen_assert(v >= 1);
-
-          if (v == 1) {
-            // Aggregate partial sums from l0 ranges.
-            aggregateL0Blocks<Alignment>();
-
-            // Apply output kernel.
-            applyOutputKernel();
-
-            // NOTE: If we call `done` callback before deleting this (context),
-            // it might deallocate Self* pointer captured by context, and we'll
-            // fail in destructor trying to deallocate temporary buffers.
-
-            // Move done call back from context before it will be destructed.
-            DoneCallback done_copy = std::move(done);
-
-            // We are confident that we are the last one who touches context.
-            delete this;
-
-            // Now safely call the done callback.
-            done_copy();
-          }
-        });
-      }
     }
 
    private:
@@ -1405,6 +1365,68 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
       }
     }
 
+    template <int Alignment>
+    void eval(Barrier& barrier, Index start_block_idx, Index end_block_idx) {
+      while (end_block_idx - start_block_idx > 1) {
+        Index mid_block_idx = (start_block_idx + end_block_idx) / 2;
+        evaluator->m_device.enqueueNoNotification(
+            [this, &barrier, mid_block_idx, end_block_idx]() {
+              eval<Alignment>(barrier, mid_block_idx, end_block_idx);
+            });
+        end_block_idx = mid_block_idx;
+      }
+
+      Index block_idx = start_block_idx;
+      Index block_start = block_idx * block_size;
+      Index block_end = block_start + actualBlockSize(block_idx);
+
+      processBlock<Alignment>(block_idx, block_start, block_end);
+      barrier.Notify();
+    }
+
+    template <int Alignment>
+    void evalAsync(Index start_block_idx, Index end_block_idx) {
+      while (end_block_idx - start_block_idx > 1) {
+        Index mid_block_idx = (start_block_idx + end_block_idx) / 2;
+        evaluator->m_device.enqueueNoNotification(
+            [this, mid_block_idx, end_block_idx]() {
+              evalAsync<Alignment>(mid_block_idx, end_block_idx);
+            });
+        end_block_idx = mid_block_idx;
+      }
+
+      Index block_idx = start_block_idx;
+
+      Index block_start = block_idx * block_size;
+      Index block_end = block_start + actualBlockSize(block_idx);
+
+      processBlock<Alignment>(block_idx, block_start, block_end);
+
+      int v = num_pending_blocks.fetch_sub(1);
+      eigen_assert(v >= 1);
+
+      if (v == 1) {
+        // Aggregate partial sums from l0 ranges.
+        aggregateL0Blocks<Alignment>();
+
+        // Apply output kernel.
+        applyOutputKernel();
+
+        // NOTE: If we call `done` callback before deleting this (context),
+        // it might deallocate Self* pointer captured by context, and we'll
+        // fail in destructor trying to deallocate temporary buffers.
+
+        // Move done call back from context before it will be destructed.
+        DoneCallback done_copy = std::move(done);
+
+        // We are confident that we are the last one who touches context.
+        delete this;
+
+        // Now safely call the done callback.
+        done_copy();
+      }
+    }
+
     // Cost model doesn't capture well the cost associated with constructing
     // tensor contraction mappers and computing loop bounds in gemm_pack_lhs
     // and gemm_pack_rhs, so we specify minimum desired block size.