[Telemetry] Improve _GetProcJiffies operation with using grep.

Previously, telemetry read the whole '/proc/timer_list' file just to parse the
first occurence of "jiffies". In case the file is big and telemetry is run
against remote device, this can create a big delay for transferring the file
to host device.

This patch modify it so that telemetry just use
'grep jiffies /proc/timer_list' to get the only lines that contain 'jiffies'.

Context: https://groups.google.com/a/chromium.org/forum/#!topic/telemetry/SblQqF0tHbc

Try job runs:
./tools/perf/run_benchmark --browser=trybot-all-android page_cycler.top_10_mobile --also-run-disabled-tests
https://codereview.chromium.org/1100233003

./tools/perf/run_benchmark --browser=trybot-all-mac page_cycler.intl_ja_zh
https://codereview.chromium.org/1106833004

./tools/perf/run_benchmark --browser=trybot-all-linux page_cycler.intl_ja_zh
https://codereview.chromium.org/1102673005

Review URL: https://codereview.chromium.org/1106043003

Cr-Commit-Position: refs/heads/master@{#326961}

3 files changed, 38 insertions, 77 deletions

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 6da1628..7e84dde 100644
--- a/tools/telemetry/telemetry/core/platform/linux_based_platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/linux_based_platform_backend.py
@@ -7,6 +7,8 @@ try:
 except ImportError:
   resource = None  # Not available on all platforms
 
+import re
+
 from telemetry.core import exceptions
 from telemetry.core.platform import platform_backend
 from telemetry import decorators
@@ -53,8 +55,7 @@ class LinuxBasedPlatformBackend(platform_backend.PlatformBackend):
     return results
 
   def GetCpuTimestamp(self):
-    timer_list = self.GetFileContents('/proc/timer_list')
-    total_jiffies = float(self._GetProcJiffies(timer_list))
+    total_jiffies = self._GetProcJiffies()
     clock_ticks = self.GetClockTicks()
     return {'TotalTime': total_jiffies / clock_ticks}
 
@@ -146,15 +147,22 @@ class LinuxBasedPlatformBackend(platform_backend.PlatformBackend):
       retval[key.strip()] = value.strip()
     return retval
 
-  def _GetProcJiffies(self, timer_list):
+  def _GetProcJiffies(self):
     """Parse '/proc/timer_list' output and returns the first jiffies attribute.
 
     Multi-CPU machines will have multiple 'jiffies:' lines, all of which will be
     essentially the same.  Return the first one."""
-    if isinstance(timer_list, str):
-      timer_list = timer_list.splitlines()
-    for line in timer_list:
-      if line.startswith('jiffies:'):
-        _, value = line.split(':')
-        return value
-    raise Exception('Unable to find jiffies from /proc/timer_list')
+    jiffies_timer_lines = self.RunCommand(
+        ['grep', 'jiffies','/proc/timer_list'])
+    if not jiffies_timer_lines:
+      raise Exception('Unable to find jiffies from /proc/timer_list')
+    jiffies_timer_list = jiffies_timer_lines.splitlines()
+    # Each line should look something like 'jiffies: 4315883489'.
+    for line in jiffies_timer_list:
+      print repr(line)
+      match = re.match('\s*jiffies\s*:\s*(\d+)', line)
+      if match:
+        value = match.group(1)
+        return float(value)
+    raise Exception('Unable to parse jiffies attribute: %s' %
+                    repr(jiffies_timer_lines))
diff --git a/tools/telemetry/telemetry/core/platform/linux_based_platform_backend_unittest.py b/tools/telemetry/telemetry/core/platform/linux_based_platform_backend_unittest.py
index 6e706a5..c76289d 100644
--- a/tools/telemetry/telemetry/core/platform/linux_based_platform_backend_unittest.py
+++ b/tools/telemetry/telemetry/core/platform/linux_based_platform_backend_unittest.py
@@ -8,6 +8,10 @@ import unittest
 from telemetry.core.platform import linux_based_platform_backend
 from telemetry.core import util
 
+util.AddDirToPythonPath(util.GetTelemetryDir(), 'third_party', 'mock')
+import mock  # pylint: disable=import-error
+
+
 
 class TestBackend(linux_based_platform_backend.LinuxBasedPlatformBackend):
 
@@ -47,11 +51,22 @@ class LinuxBasedPlatformBackendTest(unittest.TestCase):
     if not linux_based_platform_backend.resource:
       logging.warning('Test not supported')
       return
-
-    backend = TestBackend()
-    self.SetMockFileInBackend(backend, 'timer_list', '/proc/timer_list')
-    result = backend.GetCpuTimestamp()
-    self.assertEquals(result, {'TotalTime': 105054633.0})
+    jiffies_grep_string = """
+    jiffies
+jiffies  a1111
+    .last_jiffies   : 4307239958
+    .next_jiffies   : 4307239968
+    jiffies: 10505463300
+    jiffies: 10505463333
+    """
+    with mock.patch.object(
+        linux_based_platform_backend.LinuxBasedPlatformBackend,
+        'RunCommand', return_value=jiffies_grep_string) as mock_method:
+      backend = linux_based_platform_backend.LinuxBasedPlatformBackend()
+      result = backend.GetCpuTimestamp()
+      self.assertEquals(result, {'TotalTime': 105054633.0})
+    mock_method.assert_call_once_with(
+        ['grep', '-m', '1', 'jiffies:','/proc/timer_list'])
 
   def testGetMemoryStatsBasic(self):
     if not linux_based_platform_backend.resource:
diff --git a/tools/telemetry/unittest_data/timer_list b/tools/telemetry/unittest_data/timer_list
deleted file mode 100644
index d7ff169..0000000
--- a/tools/telemetry/unittest_data/timer_list
+++ /dev/null
@@ -1,62 +0,0 @@
-Timer List Version: v0.7
-HRTIMER_MAX_CLOCK_BASES: 4
-now at 49390649032656 nsecs
-
-cpu: 0
- clock 0:
-  .base:       0000000000000000
-  .index:      0
-  .resolution: 1 nsecs
-  .get_time:   ktime_get
-  .offset:     0 nsecs
-active timers:
- #0: <0000000000000000>, hrtimer_wakeup, S:01, schedule_hrtimeout_range_clock, census_census_h/2343
- # expires at 49390651724646-49390651774646 nsecs [in 2691990 to 2741990 nsecs]
- #1: <0000000000000000>, hrtimer_wakeup, S:01, schedule_hrtimeout_range_clock, census_census_h/3680
- # expires at 49390656983466-49390657033466 nsecs [in 7950810 to 8000810 nsecs]
- clock 1:
-  .base:       0000000000000000
-  .index:      1
-  .resolution: 1 nsecs
-  .get_time:   ktime_get_real
-  .offset:     1414432541083798144 nsecs
-active timers:
- #0: <0000000000000000>, hrtimer_wakeup, S:01, hrtimer_start_range_ns, mysqld/27245
- # expires at 1414481934522781000-1414481934522831000 nsecs [in 1414432543873748344 to 1414432543873798344 nsecs]
- #1: <0000000000000000>, hrtimer_wakeup, S:01, hrtimer_start_range_ns, DNS Res~ver #14/21520
- # expires at 1414482222918140000-1414482222918190000 nsecs [in 1414432832269107344 to 1414432832269157344 nsecs]
- clock 2:
-  .base:       0000000000000000
-  .index:      2
-  .resolution: 1 nsecs
-  .get_time:   ktime_get_boottime
-  .offset:     0 nsecs
-active timers:
- clock 3:
-  .base:       0000000000000000
-  .index:      3
-  .resolution: 1 nsecs
-  .get_time:   ktime_get_clocktai
-  .offset:     1414432541083798144 nsecs
-active timers:
-  .expires_next   : 49390651774646 nsecs
-  .hres_active    : 1
-  .nr_events      : 9793846
-  .nr_retries     : 580
-  .nr_hangs       : 0
-  .max_hang_time  : 0 nsecs
-  .nohz_mode      : 2
-  .last_tick      : 49390648000000 nsecs
-  .tick_stopped   : 1
-  .idle_jiffies   : 4307239958
-  .idle_calls     : 16879086
-  .idle_sleeps    : 15799778
-  .idle_entrytime : 49390647721066 nsecs
-  .idle_waketime  : 49390647714831 nsecs
-  .idle_exittime  : 49390647489308 nsecs
-  .idle_sleeptime : 44326049938322 nsecs
-  .iowait_sleeptime: 1007311574977 nsecs
-  .last_jiffies   : 4307239958
-  .next_jiffies   : 4307239968
-  .idle_expires   : 49390684000000 nsecs
-jiffies: 4307239953