Don't do parallel_pack if we can use thread_local memory in tensor contractions

1 files changed, 30 insertions, 25 deletions

diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorContractionThreadPool.h b/unsupported/Eigen/CXX11/src/Tensor/TensorContractionThreadPool.h
index 4af8d3b18..d7cd995fb 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorContractionThreadPool.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorContractionThreadPool.h
@@ -208,6 +208,23 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
     Index nm = divup(nm0, gm);
     Index nn = divup(nn0, gn);
 
+    // If there is enough concurrency in the sharding dimension, we choose not
+    // to paralellize by the other dimension, and execute all kernels in sync
+    // mode. This reduces parallelism from the nm x nn down to nn
+    // (shard_by_col==true) or nm (shard_by_col==false).
+    const Index sharding_dim_tasks = shard_by_col ? nn : nm;
+    const int num_worker_threads = this->m_device.numThreadsInPool();
+
+    // With small number of threads we want to make sure that we do not reduce
+    // parallelism too much.
+    const int oversharding_factor =
+        num_worker_threads <= 4 ? 8 :
+        num_worker_threads <= 8 ? 4 :
+        num_worker_threads <= 16 ? 2 : 1;
+
+    const bool parallelize_by_sharding_dim_only =
+        sharding_dim_tasks >= oversharding_factor * num_worker_threads;
+
     // Last by not least, decide whether we want to issue both lhs and rhs
     // packing in parallel; or issue lhs packing first, and then issue rhs
     // packing when lhs packing completes (for !shard_by_col lhs and rhs are
@@ -223,10 +240,13 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
     // But don't do it if we will use each rhs only once. Locality seems to be
     // more important in this case.
     if ((shard_by_col ? nm : nn) == 1) parallel_pack = false;
+    // Also don't get in the way of parallelize_by_sharding_dim_only
+    // optimization.
+    if (parallelize_by_sharding_dim_only) parallel_pack = false;
 
-    #define CONTEXT_ARGS                                                        \
+#define CONTEXT_ARGS                                                        \
   (this, num_threads, buffer, m, n, k, bm, bn, bk, nm, nn, nk, gm, gn, nm0, \
-   nn0, shard_by_col, parallel_pack)                                        \
+   nn0, shard_by_col, parallel_pack, parallelize_by_sharding_dim_only)      \
       .run()
 
     TENSOR_CONTRACTION_DISPATCH(Context, Alignment, CONTEXT_ARGS);
@@ -260,7 +280,7 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
     Context(const Self* self, int num_threads, Scalar* buffer, Index tm, Index tn,
             Index tk, Index bm, Index bn, Index bk, Index nm, Index nn, Index nk,
             Index gm, Index gn, Index nm0, Index nn0, bool shard_by_col,
-            bool parallel_pack)
+            bool parallel_pack, bool parallelize_by_sharding_dim_only)
         : device_(self->m_device),
           lhs_(self->m_leftImpl, self->m_left_nocontract_strides,
                self->m_i_strides, self->m_left_contracting_strides,
@@ -275,6 +295,7 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
           num_threads_(num_threads),
           shard_by_col_(shard_by_col),
           parallel_pack_(parallel_pack),
+          parallelize_by_sharding_dim_only_(parallelize_by_sharding_dim_only),
           m_(tm),
           n_(tn),
           k_(tk),
@@ -289,6 +310,9 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
           nm0_(nm0),
           nn0_(nn0)
   {
+      // These two options are mutually exclusive.
+      eigen_assert(!(parallel_pack && parallelize_by_sharding_dim_only));
+
       for (Index x = 0; x < P; x++) {
         // Normal number of notifications for k slice switch is
         // nm_ + nn_ + nm_ * nn_. However, first P - 1 slices will receive only
@@ -336,22 +360,8 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
         }
       }
 
-      // If there is enough available parallelism in sharding dimension we can
-      // call kernels in sync mode and use thread local memory for packed data.
-      const Index sharding_dim_tasks = shard_by_col ? nn : nm;
-
-      const int num_worker_threads = device_.numThreadsInPool();
-
-      // With small number of threads we want to make sure that we do not reduce
-      // parallelism too much.
-      const int oversharding_factor =
-          num_worker_threads <= 4  ? 8 :
-          num_worker_threads <= 8  ? 4 :
-          num_worker_threads <= 16 ? 2 : 1;
-
-      if (!parallel_pack_ &&
-          sharding_dim_tasks >= oversharding_factor * num_worker_threads) {
-        parallelize_by_sharding_dim_only_ = true;
+      if (parallelize_by_sharding_dim_only_) {
+        const int num_worker_threads = device_.numThreadsInPool();
 
         if (shard_by_col) {
           can_use_thread_local_packed_ = new std::atomic<bool>[nn_];
@@ -422,6 +432,7 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
     const int num_threads_;
     const bool shard_by_col_;
     const bool parallel_pack_;
+    const bool parallelize_by_sharding_dim_only_;
     // Matrix sizes.
     const Index m_;
     const Index n_;
@@ -481,12 +492,6 @@ struct TensorEvaluator<const TensorContractionOp<Indices, LeftArgType, RightArgT
     std::vector<LhsScalar*> packed_lhs_[P - 1];
     std::vector<RhsScalar*> packed_rhs_[P - 1];
 
-    // If there is enough concurrency in the sharding dimension, we choose not
-    // to paralellize by the other dimension, and execute all kernels in sync
-    // mode. This reduces parallelism from the nm_ x nn_ down to nn_
-    // (shard_by_col==true) or nm_ (shard_by_col==false).
-    bool parallelize_by_sharding_dim_only_ = false;
-
     // If we choose to parallelize only by the sharding dimension, each thread
     // will have it's own "thead local" (not a c++ thread local storage) memory
     // for packed_lhs or packed_rhs (shard_by_col = false of true). This memory