[TFLite runtime] Allow to set number of threads to TFLite interpreter (…

…apache#6901)

* Support for setting thread count in TFLite runtime,

Co-authored-by: FrozenGene <zhaowu@apache.org>

* fix lint

Co-authored-by: FrozenGene <zhaowu@apache.org>

python/tvm/contrib/tflite_runtime.py

@@ -73,6 +73,7 @@ def __init__(self, module):
         self._set_input = module["set_input"]
         self._invoke = module["invoke"]
         self._get_output = module["get_output"]
+        self._set_num_threads = module["set_num_threads"]
 
     def set_input(self, index, value):
         """Set inputs to the module via kwargs
@@ -109,3 +110,12 @@ def get_output(self, index):
             The output index
         """
         return self._get_output(index)
+
+    def set_num_threads(self, num_threads):
+        """Set the number of threads via kwargs
+        Parameters
+        ----------
+        num_threads : int
+           The number of threads
+        """
+        self._set_num_threads(num_threads)

src/runtime/contrib/tflite/tflite_runtime.cc

@@ -128,6 +128,8 @@ void TFLiteRuntime::SetInput(int index, DLTensor* data_in) {
   });
 }
 
+void TFLiteRuntime::SetNumThreads(int num_threads) { interpreter_->SetNumThreads(num_threads); }
+
 NDArray TFLiteRuntime::GetOutput(int index) const {
   TfLiteTensor* output = interpreter_->tensor(interpreter_->outputs()[index]);
   DataType dtype = TfLiteDType2TVMDType(output->type);
@@ -163,6 +165,12 @@ PackedFunc TFLiteRuntime::GetFunction(const std::string& name,
         [sptr_to_self, this](TVMArgs args, TVMRetValue* rv) { *rv = this->GetOutput(args[0]); });
   } else if (name == "invoke") {
     return PackedFunc([sptr_to_self, this](TVMArgs args, TVMRetValue* rv) { this->Invoke(); });
+  } else if (name == "set_num_threads") {
+    return PackedFunc([sptr_to_self, this](TVMArgs args, TVMRetValue* rv) {
+      int num_threads = args[0];
+      CHECK_GE(num_threads, 1);
+      this->SetNumThreads(num_threads);
+    });
   } else {
     return PackedFunc();
   }

src/runtime/contrib/tflite/tflite_runtime.h

@@ -93,6 +93,11 @@ class TFLiteRuntime : public ModuleNode {
    * \return NDArray corresponding to given output node index.
    */
   NDArray GetOutput(int index) const;
+  /*!
+   * \brief Set the number of threads available to the interpreter.
+   * \param num_threads The number of threads to be set.
+   */
+  void SetNumThreads(int num_threads);
 
   // Buffer backing the interpreter's model
   std::unique_ptr<char[]> flatBuffersBuffer_;