Add cpu_stats for the browser

tools/telemetry/telemetry/core/platform/proc_util.py

Index: tools/telemetry/telemetry/core/platform/proc_util.py
diff --git a/tools/telemetry/telemetry/core/platform/proc_util.py b/tools/telemetry/telemetry/core/platform/proc_util.py
index 656eb846996b227b9d864798f4793191f2134b15..c337cecb47a4a7609ceff705bd1a1af889ccf60d 100644
--- a/tools/telemetry/telemetry/core/platform/proc_util.py
+++ b/tools/telemetry/telemetry/core/platform/proc_util.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 os
+
 from collections import defaultdict
 
 try:
@@ -30,6 +32,26 @@ def GetSystemCommitCharge(meminfo_contents):
           - _ConvertKbToByte(meminfo['Cached']))
 
 
+def GetCpuStats(uptime, stats, add_children=False):
+  uptime = float(uptime[0])
+  utime = float(stats[13])
+  stime = float(stats[14])
+  cutime = float(stats[15])
+  cstime = float(stats[16])
+  starttime = float(stats[21])
+  hertz = float(os.sysconf(os.sysconf_names['SC_CLK_TCK'])) or 100

[tonyg, 2013/09/05 15:20:14]

Is there a way we can get the clock tick from proc instead of os? As this is
written, this method could be shared on android except for this line (because it
will return the host's frequency).

[edmundyan, 2013/09/05 18:11:19]

From some googling, not easily.  Atleast there is no direct way to access it
from /proc.  The only way I found is to take a jiffy sample before/after and
calculate the average jiffies/second.  This can be done using:

date +"%s.%N" && grep '^jiffies' /proc/timer_list

You would think /proc/uptime would work, but I'm not getting 100 from it.

For android/mac (and actually all systems) we can use ps instead.
ps -p <pid> -o cputime,etime

And just convert "[dd-]hh:mm:ss" to seconds.  It might be cleaner having all
non-windows platforms do it this way.

+
+  cpu_process_time = utime + stime
+  if add_children:
+    cpu_process_time += cutime + cstime
+  cpu_process_time_secs = cpu_process_time / hertz
+  total_time_secs = uptime - (starttime / hertz)
+
+  return {'CpuPercent': 100 * cpu_process_time_secs / total_time_secs,

[tonyg, 2013/09/05 15:20:14]

I don't think we should include this line because we'll never actually want to
know the CPU percent over the entire process lifetime. We'll only want to know
it over the course of the duration we are measuring.

The second two fields give us exactly the info needed to calculate that.

[edmundyan, 2013/09/05 18:11:19]

Shall we remove the browser unittest then?

+          'CpuProcessTime': cpu_process_time_secs,
+          'ElapsedTotalTime': total_time_secs}
+
+
 def GetMemoryStats(status_contents, stats):
   status = _GetProcFileDict(status_contents)
   if not status or not stats or 'Z' in status['State']: