Telemetry: adds CPU frequency stats.

tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py

Index: tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py
diff --git a/tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py b/tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py
index 8a7ddd0d81593fd16f8825b97c2a98c684106e4b..1de321941a02e7b1fa33c45668e044e0223df4e9 100644
--- a/tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py
@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import collections
+
 try:
   import resource  # pylint: disable=F0401
 except ImportError:
@@ -32,6 +34,24 @@ class ProcSupportingPlatformBackend(platform_backend.PlatformBackend):
     meminfo = self._GetProcFileDict(meminfo_contents)
     return self._ConvertKbToByte(meminfo['MemTotal'])
 
+  def GetGlobalCpuStats(self):
+    num_cpus = int(self._GetFileContents(
+        '/sys/devices/system/cpu/kernel_max'))
+    # Maps {frequency_in_hz: time_in_state}
+    # See https://www.kernel.org/doc/Documentation/cpu-freq/cpufreq-stats.txt
+    cpu_frequencies = collections.defaultdict(int)
+    for cpu in range(num_cpus):
+      try:
+        stats = self._GetFileContents(
+            '/sys/devices/system/cpu/cpu%d/cpufreq/stats/time_in_state' %
+            cpu)
+        for e in stats.splitlines():
+          k, v = e.split()
+          cpu_frequencies[int(k) * 1000] += int(v)
+      except IOError:
+        continue
+    return {'GlobalCpuFrequencyStats': cpu_frequencies}
+
   def GetCpuStats(self, pid):
     stats = self._GetProcFileForPid(pid, 'stat')
     if not stats: