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

build/android/pylib/perf/perf_control.py

Index: build/android/pylib/perf/perf_control.py
diff --git a/build/android/pylib/perf/perf_control.py b/build/android/pylib/perf/perf_control.py
index e13c02adf8768d6560b2d8957bdae60c148da0ae..6a636e7f37cb018b6cdd773f9b4618c9bb60da40 100644
--- a/build/android/pylib/perf/perf_control.py
+++ b/build/android/pylib/perf/perf_control.py
@@ -3,7 +3,6 @@
 # found in the LICENSE file.
 
 import logging
-import time
 
 from pylib import android_commands
 from pylib.device import device_utils
@@ -21,28 +20,30 @@ class PerfControl(object):
     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, 'Failed to detect CPUs.'
+    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():
+      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."""
@@ -58,7 +59,7 @@ class PerfControl(object):
     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',
@@ -67,7 +68,7 @@ class PerfControl(object):
             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
@@ -97,12 +98,7 @@ class PerfControl(object):
     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')