trevor-m commented on a change in pull request #8172:
URL: https://github.com/apache/tvm/pull/8172#discussion_r644156232



##########
File path: src/runtime/contrib/tensorrt/tensorrt_runtime.cc
##########
@@ -174,25 +176,50 @@ class TensorRTRuntime : public JSONRuntimeBase {
       int binding_index = engine->getBindingIndex(name.c_str());
       ICHECK_NE(binding_index, -1);
       if (data_entry_[eid]->device.device_type != kDLCUDA) {
-        
device_buffers[binding_index].CopyTo(const_cast<DLTensor*>(data_entry_[eid]));
+        auto device_buffer = GetOrAllocateDeviceBuffer(eid, binding_index);
+        device_buffer.CopyTo(const_cast<DLTensor*>(data_entry_[eid]));
       }
     }
   }
 
  private:
+  /*! \brief Get batch size for engine from the runtime input shapes. */
+  int GetBatchSize() {
+    return data_entry_[input_var_eid_[0]]->ndim == 0 ? 1 : 
data_entry_[input_var_eid_[0]]->shape[0];
+  }
+
+  /*! \brief TensorRT engines are built for a maximum batch size. If an engine 
doesn't exist for a
+   * certain batch size already, see if we can reuse an engine built for a 
higher batch size. */
+  bool FindCompatibleEngine(int batch_size, int* compatible_engine_batch_size) 
{
+    // Check for exact match
+    if (trt_engine_cache_.count(std::make_pair(symbol_name_, batch_size))) {
+      *compatible_engine_batch_size = batch_size;
+      return true;
+    }

Review comment:
       From TRT's documentation, it sounds like doing this could have 
performance impact.
   
   "Another consideration is that building the optimized network optimizes for 
the given maximum batch size. The final result will be tuned for the maximum 
batch size but will still work correctly for any smaller batch size. It is 
possible to run multiple build operations to create multiple optimized engines 
for different batch sizes, then choose which engine to use based on the actual 
batch size at runtime. "
   
   
   The implementation in this PR isn't much better because it depends on the 
order of batch sizes encountered. For example, if we encounter batch sizes 1, 
2, 4 then 3 engines are built. But if we encounter in the order 4, 2, 1, only 
one engine is built and it will be suboptimal for input sizes 1 and 2 which is 
pretty much the same result as if we only kept one engine with the largest 
batch size.
   




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