change the location of wipe cache (pytorch#24454)

Summary:
Pull Request resolved: pytorch#24454

We want to change the place of wipe_cache. From what we observed, the original place does not help.

Reviewed By: mingzhe09088

Differential Revision: D16853205

fbshipit-source-id: 1f6224a52433cbe15c0d27000b4ac140fb9cd4c3

Author: hl475

benchmarks/operator_benchmark/benchmark_core.py

@@ -171,6 +171,10 @@ def _measure_time(self, launch_test, test_case, iters):
         """
         curr_test_total_time = 0
         while True:
+            # Wipe cache
+            if self.args.wipe_cache:
+                torch.ops.operator_benchmark._clear_cache()
+
             run_time_sec = launch_test(test_case, iters)
             curr_test_total_time += run_time_sec
             # Analyze time after each run to decide if the result is stable
@@ -244,9 +248,6 @@ def run(self):
             else:
                 launch_func = self._launch_forward
 
-            if self.args.wipe_cache:
-                torch.ops.operator_benchmark._clear_cache()
-
             # Warmup
             launch_func(test_case, self.args.warmup_iterations)
             # Actual Execution