Update from https://crrev.com/305340

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'
+  _CPU_PATH = '/sys/devices/system/cpu'
   _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)
+    # this will raise an AdbShellCommandFailedError if no CPU files are found
+    self._cpu_files = self._device.RunShellCommand(
+        'ls -d cpu[0-9]*', cwd=self._CPU_PATH, check_return=True, as_root=True)
+    assert self._cpu_files, 'Failed to detect CPUs.'
+    self._cpu_file_list = ' '.join(self._cpu_files)
+    logging.info('CPUs found: %s', self._cpu_file_list)
     self._have_mpdecision = self._device.FileExists('/system/bin/mpdecision')
 
   def SetHighPerfMode(self):
     """Sets the highest stable 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)
@@ skipping 39 matching lines @@
         'GT-I9300': 'pegasusq',
         'Galaxy Nexus': 'interactive',
         'Nexus 4': 'ondemand',
         'Nexus 5': 'ondemand',
         'Nexus 7': 'interactive',
         'Nexus 10': 'interactive'
     }.get(product_model, 'ondemand')
     self._SetScalingGovernorInternal(governor_mode)
     self._ForceAllCpusOnline(False)
 
+  def GetCpuInfo(self):
+    online = (output.rstrip() == '1' and status == 0
+              for (_, output, status) in self._ForEachCpu('cat "$CPU/online"'))
+    governor = (output.rstrip() if status == 0 else None
+                for (_, output, status)
+                in self._ForEachCpu('cat "$CPU/cpufreq/scaling_governor"'))
+    return zip(self._cpu_files, online, governor)
+
+  def _ForEachCpu(self, cmd):
+    script = '; '.join([
+        'for CPU in %s' % self._cpu_file_list,
+        'do %s' % cmd,
+        'echo -n "%~%$?%~%"',
+        'done'
+    ])
+    output = self._device.RunShellCommand(
+        script, cwd=self._CPU_PATH, check_return=True, as_root=True)
+    output = '\n'.join(output).split('%~%')
+    return zip(self._cpu_files, output[0::2], (int(c) for c in output[1::2]))
+
+  def _WriteEachCpuFile(self, path, value):
+    results = self._ForEachCpu(
+        'test -e "$CPU/{path}" && echo {value} > "$CPU/{path}"'.format(
+            path=path, value=value))
+    cpus = ' '.join(cpu for (cpu, _, status) in results if status == 0)
+    if cpus:
+      logging.info('Successfully set %s to %r on: %s', path, value, cpus)
+    else:
+      logging.warning('Failed to set %s to %r on any cpus')
+
   def _SetScalingGovernorInternal(self, value):
-    cpu_cores = ' '.join([str(x) for x in range(self._num_cpu_cores)])
-    script = ('for CPU in %s; do\n'
-        '  FILE="/sys/devices/system/cpu/cpu$CPU/cpufreq/scaling_governor"\n'
-        '  test -e $FILE && echo %s > $FILE\n'
-        'done\n') % (cpu_cores, value)
-    logging.info('Setting scaling governor mode: %s', value)
-    self._device.RunShellCommand(script, as_root=True)
+    self._WriteEachCpuFile('cpufreq/scaling_governor', value)
 
   def _SetScalingMaxFreq(self, value):
-    cpu_cores = ' '.join([str(x) for x in range(self._num_cpu_cores)])
-    script = ('for CPU in %s; do\n'
-        '  FILE="/sys/devices/system/cpu/cpu$CPU/cpufreq/scaling_max_freq"\n'
-        '  test -e $FILE && echo %d > $FILE\n'
-        'done\n') % (cpu_cores, value)
-    self._device.RunShellCommand(script, as_root=True)
+    self._WriteEachCpuFile('cpufreq/scaling_max_freq', '%d' % value)
 
   def _SetMaxGpuClock(self, value):
     self._device.WriteFile('/sys/class/kgsl/kgsl-3d0/max_gpuclk',
                            str(value),
                            as_root=True)
 
   def _AllCpusAreOnline(self):
-    for cpu in range(1, self._num_cpu_cores):
-      online_path = PerfControl._CPU_ONLINE_FMT % cpu
-      # TODO(epenner): Investigate why file may be missing
-      # (http://crbug.com/397118)
-      if not self._device.FileExists(online_path) or \
-            self._device.ReadFile(online_path)[0] == '0':
-        return False
-    return True
+    results = self._ForEachCpu('cat "$CPU/online"')
+    # TODO(epenner): Investigate why file may be missing
+    # (http://crbug.com/397118)
+    return all(output.rstrip() == '1' and status == 0
+               for (cpu, output, status) in results
+               if cpu != 'cpu0')
 
   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, as_root=True)
+      self._device.RunShellCommand(script, check_return=True, as_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._num_cpu_cores):
-      online_path = PerfControl._CPU_ONLINE_FMT % cpu
-      self._device.WriteFile(online_path, '1', as_root=True)
-
+    if force_online:
+      self._ForEachCpu('echo 1 > "$CPU/online"')