Telemetry: Don't fail on setting performance mode without root.

build/android/pylib/perf/perf_control.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import atexit
 import logging
 
 from pylib import android_commands
 from pylib.device import device_utils
 
-
 class PerfControl(object):
   """Provides methods for setting the performance mode of a device."""
   _SCALING_GOVERNOR_FMT = (
       '/sys/devices/system/cpu/cpu%d/cpufreq/scaling_governor')
   _CPU_ONLINE_FMT = '/sys/devices/system/cpu/cpu%d/online'
   _KERNEL_MAX = '/sys/devices/system/cpu/kernel_max'
 
   def __init__(self, device):
     # TODO(jbudorick) Remove once telemetry gets switched over.
     if isinstance(device, android_commands.AndroidCommands):
       device = device_utils.DeviceUtils(device)
     self._device = device
     cpu_files = self._device.RunShellCommand(
       'ls -d /sys/devices/system/cpu/cpu[0-9]*')
     self._num_cpu_cores = len(cpu_files)
     assert self._num_cpu_cores > 0, 'Failed to detect CPUs.'
     logging.info('Number of CPUs: %d', self._num_cpu_cores)
     self._have_mpdecision = self._device.FileExists('/system/bin/mpdecision')
 
   def SetHighPerfMode(self):
+    """Sets the highest possible performance mode for the device."""
+    if not self._device.old_interface.IsRootEnabled():
+      message = 'Need root for performance mode. Results may be NOISY!!'
+      logging.warning(message)
+      # Add an additional warning at exit, such that it's clear that any results
+      # may be different/noisy (due to the lack of intended performance mode).
+      atexit.register(logging.warning, message)
+      return
     # TODO(epenner): Enable on all devices (http://crbug.com/383566)
     if 'Nexus 4' == self._device.old_interface.GetProductModel():
       self._ForceAllCpusOnline(True)
       if not self._AllCpusAreOnline():
-        logging.warning('Failed to force CPUs online. Results may be noisy!')
+        logging.warning('Failed to force CPUs online. Results may be NOISY!')
     self._SetScalingGovernorInternal('performance')
 
   def SetPerfProfilingMode(self):
-    """Sets the highest possible performance mode for the device."""
+    """Enables all cores for reliable perf profiling."""
     self._ForceAllCpusOnline(True)
     self._SetScalingGovernorInternal('performance')
     if not self._AllCpusAreOnline():
       if not self._device.old_interface.IsRootEnabled():
         raise RuntimeError('Need root to force CPUs online.')
       raise RuntimeError('Failed to force CPUs online.')
 
   def SetDefaultPerfMode(self):
     """Sets the performance mode for the device to its default mode."""
+    if not self._device.old_interface.IsRootEnabled():
+      return
     product_model = self._device.GetProp('ro.product.model')
     governor_mode = {
         'GT-I9300': 'pegasusq',
         'Galaxy Nexus': 'interactive',
         'Nexus 4': 'ondemand',
         'Nexus 7': 'interactive',
         'Nexus 10': 'interactive'
     }.get(product_model, 'ondemand')
     self._SetScalingGovernorInternal(governor_mode)
     self._ForceAllCpusOnline(False)
@@ skipping 36 matching lines @@
 
     if not self._have_mpdecision and not self._AllCpusAreOnline():
       logging.warning('Unexpected cpu hot plugging detected.')
 
     if not force_online:
       return
 
     for cpu in range(self._num_cpu_cores):
       online_path = PerfControl._CPU_ONLINE_FMT % cpu
       self._device.WriteFile(online_path, '1', as_root=True)