Telemetry: Implement idle wakeups counting on Android.

tools/telemetry/telemetry/core/platform/linux_based_platform_backend.py

Index: tools/telemetry/telemetry/core/platform/linux_based_platform_backend.py
diff --git a/tools/telemetry/telemetry/core/platform/linux_based_platform_backend.py b/tools/telemetry/telemetry/core/platform/linux_based_platform_backend.py
index 9255303fc027f09f22b0b5ab57a2d260e5129150..d595f7ab20aebcef0d636d503f9cf6cd70f30fb4 100644
--- a/tools/telemetry/telemetry/core/platform/linux_based_platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/linux_based_platform_backend.py
@@ -10,6 +10,7 @@ except ImportError:
 from telemetry import decorators
 from telemetry.core import exceptions
 from telemetry.core.platform import platform_backend
+from telemetry.core.platform import process_statistic_timeline_data
 
 
 class LinuxBasedPlatformBackend(platform_backend.PlatformBackend):
@@ -50,6 +51,8 @@ class LinuxBasedPlatformBackend(platform_backend.PlatformBackend):
     cpu_process_jiffies = utime + stime
     clock_ticks = self.GetClockTicks()
     results.update({'CpuProcessTime': cpu_process_jiffies / clock_ticks})
+    if self.CanMeasureIdleWakeUps():
+      results.update({'IdleWakeupCount': self._GetIdleWakeupCount(pid)})
     return results
 
   def GetCpuTimestamp(self):
@@ -109,6 +112,12 @@ class LinuxBasedPlatformBackend(platform_backend.PlatformBackend):
   def RunCommand(self, cmd):
     raise NotImplementedError()
 
+  def StartMeasuringIdleWakeUps(self):
+    self._EnableTimerStatsCollection(True)
+
+  def StopMeasuringIdleWakeUps(self):
+    self._EnableTimerStatsCollection(False)
+
   @staticmethod
   def ParseCStateSample(sample):
     """Parse a single c-state residency sample.
@@ -129,6 +138,30 @@ class LinuxBasedPlatformBackend(platform_backend.PlatformBackend):
     assert pid, 'pid is required'
     return bool(self.GetPsOutput(['pid'], pid) == str(pid))
 
+  def _GetIdleWakeupCount(self, pid):
+    """Find the given pid in the timer_stats and sum up the wake-up count.
+
+    Each row is in the form of: wake_up_count, pid process_name reason
+    Due to possibly multiple reasons, a given pid can appear in multiple rows.
+    """
+    contents = self.GetFileContents('/proc/timer_stats')
+    count = 0
+    split_lines = contents.splitlines()
+    for line in split_lines[:-1]:
+      line_split = line.split(',', 1)
+      if len(line_split) < 2:
+        continue
+      count_str, rest_str = line_split
+      current_pid = int(rest_str.strip().split(' ')[0])
+      if current_pid == pid:
+        count += int(count_str.strip())
+    return process_statistic_timeline_data.IdleWakeupTimelineData(pid, count)
+
+  def _EnableTimerStatsCollection(self, enable):
+    """Writes to /proc/timer_stats to start/stop measuring process wakeups."""
+    # TODO(thestig) Implement on Linux and CrOS.
+    raise NotImplementedError()
+
   def _GetProcFileForPid(self, pid, filename):
     try:
       return self.GetFileContents('/proc/%s/%s' % (pid, filename))