Prefix inaccurate costs with "~" in VirtualScheduler verbose log.

Fix some inaccurate estimates exposed by this approach:
- propagate the inaccuracy flag when merging device stats;
- estimate Const as no-op;
- estimate RandomUniform, Relu and Softmax as element-wise;
- consider estimates accurate for known element-wise ops in op_level_cost_estimator.

PiperOrigin-RevId: 177643976

1 files changed, 4 insertions, 4 deletions

diff --git a/tensorflow/core/grappler/costs/op_level_cost_estimator.h b/tensorflow/core/grappler/costs/op_level_cost_estimator.h
index 3a8385dd73..c6f23ee0aa 100644
--- a/tensorflow/core/grappler/costs/op_level_cost_estimator.h
+++ b/tensorflow/core/grappler/costs/op_level_cost_estimator.h
@@ -45,11 +45,11 @@ class OpLevelCostEstimator {
   // Returns basic device performance info.
   virtual DeviceInfo GetDeviceInfo(const DeviceProperties& device) const;
 
-  // For operations for which we haven't yet built estimates, returns a dummy
-  // value based on input size.
-  Costs DummyExecutionTime(const OpContext& op_context) const;
+  // Predict cost of an op for which no accurate estimator is defined.
+  Costs PredictCostOfAnUnknownOp(const OpContext& op_context) const;
 
-  // Naive cost estimate based on operations divided by device ops/sec.
+  // Naive cost estimate based on operations divided by device ops/sec,
+  // and input/output tensor sizes.
   Costs PredictOpCountBasedCost(double operations,
                                 const OpInfo& op_features) const;