Increase mimimum number of warmup runs to 2 (#58801)

Summary:
The JIT will typically need two warmup runs to do profiling and optimization.
This is not the perfect solution but it will substantially reduce the number of surprised people when the docs say torch.utils.benchmark.Timer takes care of warmup.

Pull Request resolved: #58801

Reviewed By: desertfire

Differential Revision: D28644244

Pulled By: robieta

fbshipit-source-id: cc54ed019e882a379d6e4a0c6a01fd5873dd41c3

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,