Increase mimimum number of warmup runs to 2

The JIT will typically need two warmup runs to do profiling and
optimization.

torch/utils/benchmark/utils/timer.py

@@ -259,7 +259,7 @@ def timeit(self, number: int = 1000000) -> common.Measurement:
         """
         with common.set_torch_threads(self._task_spec.num_threads):
             # Warmup
-            self._timer.timeit(number=max(int(number // 100), 1))
+            self._timer.timeit(number=max(int(number // 100), 2))
 
             return common.Measurement(
                 number_per_run=number,