Update from https://crrev.com/305340

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 ede131789d70faca081d3810e5ccafb659adfb07..73cf95c53608591365b0335ff1aca2218f03d4d4 100644
--- a/build/android/pylib/perf/perf_control.py
+++ b/build/android/pylib/perf/perf_control.py
@@ -10,9 +10,7 @@ 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):
@@ -20,11 +18,12 @@ class PerfControl(object):
     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):
@@ -84,22 +83,41 @@ class PerfControl(object):
     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',
@@ -107,14 +125,12 @@ class PerfControl(object):
                            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.
@@ -132,15 +148,10 @@ class PerfControl(object):
     """
     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"')