TELEMETRY: Don't always fail test when forcing CPUs fails.

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 logging
-import time
 
 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
-    kernel_max = self._device.old_interface.GetFileContents(
-        PerfControl._KERNEL_MAX, log_result=False)
-    assert kernel_max, 'Unable to find %s' % PerfControl._KERNEL_MAX
-    self._kernel_max = int(kernel_max[0])
-    logging.info('Maximum CPU index: %d', self._kernel_max)
+    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

[tonyg, 2014/06/24 02:16:54]

We should add an error message to this assert.

[epennerAtGoogle, 2014/06/24 02:35:57]

Done.

+    logging.info('Number of CPUs: %d', self._num_cpu_cores)
     self._have_mpdecision = self._device.old_interface.FileExistsOnDevice(
         '/system/bin/mpdecision')
 
-  @property
-  def _NumCpuCores(self):
-    return self._kernel_max + 1
-
   def SetHighPerfMode(self):
     # 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!')
     self._SetScalingGovernorInternal('performance')
 
   def SetPerfProfilingMode(self):
     """Sets the highest possible performance mode for the device."""
     self._ForceAllCpusOnline(True)
     self._SetScalingGovernorInternal('performance')
+    if not self._AllCpusAreOnline():
+      raise RuntimeError('Failed to force CPUs online. Can you adb root?')

[tonyg, 2014/06/24 02:16:54]

We have methods that do this in android_commands.py: IsRootEnabled() and
EnableAdbRoot(). Should we just try to run that for them if not root, or fail
hard if root?

[epennerAtGoogle, 2014/06/24 02:35:57]

The current check catches other problems, however the message is not clear
indeed. I broke this into two cases. If the CPUs are not online, I first check
for root and give a clear error message about that. Then fall back on the more
ambiguous error.

 
   def SetDefaultPerfMode(self):
     """Sets the performance mode for the device to its default mode."""
     product_model = self._device.old_interface.GetProductModel()
     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)
 
   def _SetScalingGovernorInternal(self, value):
-    for cpu in range(self._NumCpuCores):
+    for cpu in range(self._num_cpu_cores):
       scaling_governor_file = PerfControl._SCALING_GOVERNOR_FMT % cpu
       if self._device.old_interface.FileExistsOnDevice(scaling_governor_file):
         logging.info('Writing scaling governor mode \'%s\' -> %s',
                      value, scaling_governor_file)
         self._device.old_interface.SetProtectedFileContents(
             scaling_governor_file, value)
 
   def _AllCpusAreOnline(self):
-    for cpu in range(self._NumCpuCores):
+    for cpu in range(self._num_cpu_cores):
       online_path = PerfControl._CPU_ONLINE_FMT % cpu
       if self._device.old_interface.GetFileContents(online_path)[0] == '0':
         return False
     return True
 
   def _ForceAllCpusOnline(self, force_online):
     """Enable all CPUs on a device.
 
     Some vendors (or only Qualcomm?) hot-plug their CPUs, which can add noise
     to measurements:
     - In perf, samples are only taken for the CPUs that are online when the
       measurement is started.
     - The scaling governor can't be set for an offline CPU and frequency scaling
       on newly enabled CPUs adds noise to both perf and tracing measurements.
 
     It appears Qualcomm is the only vendor that hot-plugs CPUs, and on Qualcomm
     this is done by "mpdecision".
 
     """
     if self._have_mpdecision:
       script = 'stop mpdecision' if force_online else 'start mpdecision'
       self._device.RunShellCommand(script, root=True)
 
     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._NumCpuCores):
+    for cpu in range(self._num_cpu_cores):
       online_path = PerfControl._CPU_ONLINE_FMT % cpu
       self._device.old_interface.SetProtectedFileContents(
           online_path, '1')
-
-    # Double check all cores stayed online.
-    time.sleep(0.25)
-    if not self._AllCpusAreOnline():
-      raise RuntimeError('Failed to force CPUs online')