Telemetry: manage CPU core online state for some device types

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 92aaa2433012499b4b78ab5682b557fc69eae604..7952656f9e334df00dfccbf2ecb976d1e8bd6d53 100644
--- a/build/android/pylib/perf/perf_control.py
+++ b/build/android/pylib/perf/perf_control.py
@@ -6,13 +6,24 @@
 import logging
 from pylib import android_commands
 from pylib.device import device_utils
+import time
 
 
 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')
+
   _KERNEL_MAX = '/sys/devices/system/cpu/kernel_max'
+  _CPU_DIR_FMT = '/sys/devices/system/cpu/cpu%d/'
+  _SCALING_GOVERNOR_FMT = _CPU_DIR_FMT + 'cpufreq/scaling_governor'
+  _CPU_ONLINE_FMT = _CPU_DIR_FMT + 'online'
+  _SCALING_FREQUENCY_STAT_NAMES = [
+      'cpufreq/scaling_min_freq',
+      'cpufreq/scaling_max_freq',
+      'cpufreq/scaling_cur_freq',
+  ]
+  _MODELS_TO_FULLY_MANAGED_CPU_INDEXES = {
+    'Nexus 4': [0, 1, 2, 3],
+  }
 
   def __init__(self, device):
     # TODO(jbudorick) Remove once telemetry gets switched over.
@@ -28,33 +39,120 @@ class PerfControl(object):
         self._device.old_interface.GetFileContents(
             PerfControl._SCALING_GOVERNOR_FMT % 0,
             log_result=False)[0]
+    self._LogCurrentCpuFrequencyInfo()
+
+    # Bring CPUs online/offline on some device types to reduce variance in
+    # performance measurements.  Other device types are either hard to fully
+    # manage properly or we did not decide what settings look 'typical' for
+    # them. 'Galaxy Nexus' and 'Nexus 10' seem to use both cores all time
+    # without hotplugging them with PerfControl, but we still may need to manage
+    # their frequency later. TODO(pasko): manage Nexus 7 CPUs with PerfControl,
+    # v1 and v2 differ significantly.
+    #
+    # *Not fully managing* CPUs means that only a subset of CPU properties
+    # are updated (scaling governor only now) and only for those CPUs
+    # represented by sysfs at the moment (/sys/devices/system/cpu/cpuX/...)
+    self._fully_managed_cpus = (
+        self._MODELS_TO_FULLY_MANAGED_CPU_INDEXES.get(
+            self._device.old_interface.GetProductModel(), []))
+    if self._fully_managed_cpus:
+      self._cpus_on_originally = []
+      for cpu in xrange(self._kernel_max + 1):
+        if '1' in self._GetFileContents(
+            PerfControl._CPU_ONLINE_FMT % cpu):
+          self._cpus_on_originally.append(cpu)
+
+  def _BringCpuOffline(self, cpu_index):
+    logging.info('Bringing CPU #%d offline.', cpu_index)
+    self._device.old_interface.SetFileContents(
+        PerfControl._CPU_ONLINE_FMT % cpu_index, '0')
+
+  def _BringCpuOnline(self, cpu_index):
+    "Brings a CPU core online, waits for it to show up in sysfs."
+
+    logging.info('Bringing CPU #%d online.' %cpu_index)
+    times_to_wait_left = 5
+    cpu_online_file = PerfControl._CPU_ONLINE_FMT % cpu_index
+    while (True):
+      self._device.old_interface.SetFileContents(cpu_online_file, '1')
+      if '1' in self._GetFileContents(cpu_online_file):
+        break
+      if times_to_wait_left == 0:
+        logging.warning('Gave up bringing CPU %d online', cpu_index)
+        break
+      times_to_wait_left -= 1
+      logging.warning('Could not bring CPU %d online, retrying..',
+          cpu_index)
+      time.sleep(0.1)
+
+  def _GetFileContents(self, file_name):
+    return '\n'.join(self._device.old_interface.GetFileContents(file_name))
+
+  def _LogCurrentCpuFrequencyInfo(self):
+    for cpu in xrange(self._kernel_max + 1):
+      for stat_name in PerfControl._SCALING_FREQUENCY_STAT_NAMES:
+        stat_file_name = (PerfControl._CPU_DIR_FMT + stat_name) % cpu
+        if self._device.old_interface.FileExistsOnDevice(stat_file_name):
+          info = self._GetFileContents(stat_file_name)
+          logging.info('CPU #%d frequency info: %s: %s', cpu, stat_name, info)
 
   def SetHighPerfMode(self):
     """Sets the highest possible performance mode for the device."""
-    self._SetScalingGovernorInternal('performance')
+
+    if not self._fully_managed_cpus:
+      for cpu in xrange(self._kernel_max + 1):
+        self._SetScalingGovernorInternal(cpu, 'performance')
+    else:
+      # Stop the 'mpdecision' hotplug manager to get a constant number of CPUs
+      # online when running tests. TODO(pasko): stop 'thermald'.
+      self._device.old_interface.RunShellCommand('stop mpdecision')
+      for cpu in xrange(self._kernel_max + 1):
+        if cpu in self._fully_managed_cpus:
+          self._BringCpuOnline(cpu)
+          self._SetScalingGovernorInternal(cpu, 'performance')
+        else:
+          self._BringCpuOffline(cpu)
 
   def SetDefaultPerfMode(self):
     """Sets the performance mode for the device to its default mode."""
+    self._LogCurrentCpuFrequencyInfo()
     product_model = self._device.old_interface.GetProductModel()
     governor_mode = {
         '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)
+    if not self._fully_managed_cpus:
+      # Set the default perf mode only if no CPUs were forced online.
+      for cpu in xrange(self._kernel_max + 1):
+        self._SetScalingGovernorInternal(cpu, governor_mode)
+    # If 'mpdecision' is present on the system, it will manage CPU
+    # online/offline state, otherwise it is a no-op.
+    self._device.old_interface.RunShellCommand('start mpdecision')
 
   def RestoreOriginalPerfMode(self):
     """Resets the original performance mode of the device."""
-    self._SetScalingGovernorInternal(self._original_scaling_governor)
-
-  def _SetScalingGovernorInternal(self, value):
-    for cpu in range(self._kernel_max + 1):
-      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)
+    self._LogCurrentCpuFrequencyInfo()
+    if not self._fully_managed_cpus:
+      for cpu in xrange(self._kernel_max + 1):
+        self._SetScalingGovernorInternal(cpu, self._original_scaling_governor)
+    else:
+      for cpu in xrange(self._kernel_max + 1):
+        if cpu in self._cpus_on_originally:
+          self._BringCpuOnline(cpu)
+          self._SetScalingGovernorInternal(cpu, self._original_scaling_governor)
+        else:
+          self._SetScalingGovernorInternal(cpu, self._original_scaling_governor)
+          self._BringCpuOffline(cpu)
+      self._device.old_interface.RunShellCommand('start mpdecision')
 
+  def _SetScalingGovernorInternal(self, cpu, value):
+    scaling_governor_file = PerfControl._SCALING_GOVERNOR_FMT % cpu
+    if (self._fully_managed_cpus or
+        self._device.old_interface.FileExistsOnDevice(scaling_governor_file)):
+      logging.info('Writing scaling governor mode "%s" -> %s',
+                   value, scaling_governor_file)
+      self._device.old_interface.SetFileContents(scaling_governor_file, value)