Telemetry: Linux-based backends should return CPU results in seconds, not jiffies.

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 cb031755c3588b3880e3f069b014bb2a0fb95d8f..9255303fc027f09f22b0b5ab57a2d260e5129150 100644
--- a/tools/telemetry/telemetry/core/platform/linux_based_platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/linux_based_platform_backend.py
@@ -14,7 +14,9 @@ from telemetry.core.platform import platform_backend
 
 class LinuxBasedPlatformBackend(platform_backend.PlatformBackend):
 
-  """Abstract platform containing functionality shared by all linux based OSes.
+  """Abstract platform containing functionality shared by all Linux based OSes.
+
+  This includes Android and ChromeOS.
 
   Subclasses must implement RunCommand, GetFileContents, GetPsOutput, and
   ParseCStateSample."""
@@ -38,19 +40,23 @@ class LinuxBasedPlatformBackend(platform_backend.PlatformBackend):
     return self._ConvertKbToByte(meminfo['MemTotal'])
 
   def GetCpuStats(self, pid):
+    results = {}
     stats = self._GetProcFileForPid(pid, 'stat')
     if not stats:
-      return {}
+      return results
     stats = stats.split()
     utime = float(stats[13])
     stime = float(stats[14])
     cpu_process_jiffies = utime + stime
-    return {'CpuProcessTime': cpu_process_jiffies}
+    clock_ticks = self.GetClockTicks()
+    results.update({'CpuProcessTime': cpu_process_jiffies / clock_ticks})
+    return results
 
   def GetCpuTimestamp(self):
     timer_list = self.GetFileContents('/proc/timer_list')
     total_jiffies = float(self._GetProcJiffies(timer_list))
-    return {'TotalTime': total_jiffies}
+    clock_ticks = self.GetClockTicks()
+    return {'TotalTime': total_jiffies / clock_ticks}
 
   def GetMemoryStats(self, pid):
     status_contents = self._GetProcFileForPid(pid, 'status')
@@ -84,6 +90,16 @@ class LinuxBasedPlatformBackend(platform_backend.PlatformBackend):
             'ReadTransferCount': int(io['rchar']),
             'WriteTransferCount': int(io['wchar'])}
 
+  @decorators.Cache
+  def GetClockTicks(self):
+    """Returns the number of clock ticks per second.
+
+    The proper way is to call os.sysconf('SC_CLK_TCK') but that is not easy to
+    do on Android/CrOS. In practice, nearly all Linux machines have a USER_HZ
+    of 100, so just return that.
+    """
+    return 100
+
   def GetFileContents(self, filename):
     raise NotImplementedError()