Add retain-output argument (#145921)

Summary:
This PR add retain-output argument which enables appending to the already existing output file if it exists instead of deleting it and creating a new one.

X-link: pytorch/pytorch#145921
Approved by: https://github.com/jansel

Reviewed By: ZainRizvi, atalman

Differential Revision: D69208159

fbshipit-source-id: 0d635d89a697157185fdb22999ccf7daea6319f4

Author: generatedunixname499836121

userbenchmark/dynamo/dynamobench/common.py

@@ -3229,6 +3229,13 @@ def get_example_inputs(self):
         help="Enables Memory Snapshot tool for memory deep dives: https://pytorch.org/blog/understanding-gpu-memory-1/",
     )
 
+    parser.add_argument(
+        "--retain-output",
+        action="store_true",
+        help="Enables appending to the already existing output file if it exists \
+            instead of deleting it and creating a new one.",
+    )
+
     group_latency = parser.add_mutually_exclusive_group()
     group_latency.add_argument(
         "--cold-start-latency",
@@ -4078,7 +4085,11 @@ def detect_and_mark_batch(t):
             )
     else:
         metrics.purge_old_log_files()
-        if output_filename and os.path.exists(output_filename):
+        if (
+            output_filename
+            and os.path.exists(output_filename)
+            and not args.retain_output
+        ):
             os.unlink(output_filename)
         if original_dir:
             os.chdir(original_dir)