[Android benchmark] introduce warm up iterations

Differential Revision: D70017241

Pull Request resolved: pytorch#8626

Author: kirklandsign

extension/benchmark/android/benchmark/app/src/main/java/org/pytorch/minibench/BenchmarkActivity.java

@@ -44,6 +44,7 @@ protected void onCreate(Bundle savedInstanceState) {
             .get();
 
     int numIter = intent.getIntExtra("num_iter", 50);
+    int numWarmupIter = intent.getIntExtra("num_warm_up_iter", 5);
 
     // TODO: Format the string with a parsable format
     Stats stats = new Stats();
@@ -58,6 +59,10 @@ protected Void doInBackground(Void... voids) {
         stats.errorCode = module.loadMethod("forward");
         stats.loadEnd = System.nanoTime();
 
+        for (int i = 0; i < numWarmupIter; i++) {
+          module.forward();
+        }
+
         for (int i = 0; i < numIter; i++) {
           long start = System.nanoTime();
           module.forward();