diff --git a/android/pylib/perf/setup.py b/android/pylib/perf/setup.py
index 74bf79fdd..39e50980d 100644
--- a/android/pylib/perf/setup.py
+++ b/android/pylib/perf/setup.py
@@ -10,6 +10,7 @@ import logging
 import os
 import psutil
 import signal
+import shutil
 import time
 
 from pylib import android_commands
@@ -58,8 +59,9 @@ def Setup(test_options):
   Returns:
     A tuple of (TestRunnerFactory, tests).
   """
-  if not os.path.exists(constants.PERF_OUTPUT_DIR):
-    os.makedirs(constants.PERF_OUTPUT_DIR)
+  if os.path.exists(constants.PERF_OUTPUT_DIR):
+    shutil.rmtree(constants.PERF_OUTPUT_DIR)
+  os.makedirs(constants.PERF_OUTPUT_DIR)
 
   # Before running the tests, kill any leftover server.
   _KillPendingServers()
diff --git a/android/pylib/perf/test_runner.py b/android/pylib/perf/test_runner.py
index 10a8da2d4..e3648f74a 100644
--- a/android/pylib/perf/test_runner.py
+++ b/android/pylib/perf/test_runner.py
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-"""Runs a perf test on a single device.
+"""Runs perf tests.
 
 Our buildbot infrastructure requires each slave to run steps serially.
 This is sub-optimal for android, where these steps can run independently on
@@ -93,11 +93,24 @@ class TestRunner(base_test_runner.BaseTestRunner):
     self._tests = tests
     self._flaky_tests = flaky_tests
 
+  @staticmethod
+  def _IsBetter(result):
+    if result['actual_exit_code'] == 0:
+      return True
+    pickled = os.path.join(constants.PERF_OUTPUT_DIR,
+                           result['name'])
+    if not os.path.exists(pickled):
+      return True
+    with file(pickled, 'r') as f:
+      previous = pickle.loads(f.read())
+    return result['actual_exit_code'] < previous['actual_exit_code']
+
   @staticmethod
   def _SaveResult(result):
-    with file(os.path.join(constants.PERF_OUTPUT_DIR,
-                           result['name']), 'w') as f:
-      f.write(pickle.dumps(result))
+    if TestRunner._IsBetter(result):
+      with file(os.path.join(constants.PERF_OUTPUT_DIR,
+                             result['name']), 'w') as f:
+        f.write(pickle.dumps(result))
 
   def _LaunchPerfTest(self, test_name):
     """Runs a perf test.
@@ -133,6 +146,7 @@ class TestRunner(base_test_runner.BaseTestRunner):
     result_type = base_test_result.ResultType.FAIL
     if exit_code == 0:
       result_type = base_test_result.ResultType.PASS
+    actual_exit_code = exit_code
     if test_name in self._flaky_tests:
       # The exit_code is used at the second stage when printing the
       # test output. If the test is flaky, force to "0" to get that step green
@@ -144,6 +158,7 @@ class TestRunner(base_test_runner.BaseTestRunner):
         'name': test_name,
         'output': output,
         'exit_code': exit_code,
+        'actual_exit_code': actual_exit_code,
         'result_type': result_type,
         'total_time': (end_time - start_time).seconds,
         'device': self.device,