tools/perf/metrics/cpu.py

   1 # Copyright 2013 The Chromium Authors. All rights reserved.
   2 # Use of this source code is governed by a BSD-style license that can be
   3 # found in the LICENSE file.
   4
   5 from telemetry.value import scalar
   6
   7 from metrics import Metric
   8
   9
  10 class CpuMetric(Metric):
  11   """Calulates CPU load over a span of time."""
  12
  13   def __init__(self, browser):
  14     super(CpuMetric, self).__init__()
  15     self._browser = browser
  16     self._start_cpu = None
  17     self._stop_cpu = None
  18
  19   def DidStartBrowser(self, browser):
  20     # Save the browser object so that cpu_stats can be accessed later.
  21     self._browser = browser
  22
  23   def Start(self, page, tab):
  24     self._start_cpu = self._browser.cpu_stats
  25
  26   def Stop(self, page, tab):
  27     assert self._start_cpu, 'Must call Start() first'
  28     self._stop_cpu = self._browser.cpu_stats
  29
  30   # Optional argument trace_name is not in base class Metric.
  31   # pylint: disable=W0221
  32   def AddResults(self, tab, results, trace_name='cpu_utilization'):
  33     assert self._stop_cpu, 'Must call Stop() first'
  34     cpu_stats = _SubtractCpuStats(self._stop_cpu, self._start_cpu)
  35
  36     # FIXME: Renderer process CPU times are impossible to compare correctly.
  37     # http://crbug.com/419786#c11
  38     if 'Renderer' in cpu_stats:
  39       del cpu_stats['Renderer']
  40
  41     # Add a result for each process type.
  42     for process_type in cpu_stats:
  43       trace_name_for_process = '%s_%s' % (trace_name, process_type.lower())
  44       cpu_percent = 100 * cpu_stats[process_type]
  45       results.AddValue(scalar.ScalarValue(
  46           results.current_page, 'cpu_utilization.%s' % trace_name_for_process,
  47           '%', cpu_percent, important=False))
  48
  49
  50 def _SubtractCpuStats(cpu_stats, start_cpu_stats):
  51   """Computes average cpu usage over a time period for different process types.
  52
  53   Each of the two cpu_stats arguments is a dict with the following format:
  54       {'Browser': {'CpuProcessTime': ..., 'TotalTime': ...},
  55        'Renderer': {'CpuProcessTime': ..., 'TotalTime': ...}
  56        'Gpu': {'CpuProcessTime': ..., 'TotalTime': ...}}
  57
  58   The 'CpuProcessTime' fields represent the number of seconds of CPU time
  59   spent in each process, and total time is the number of real seconds
  60   that have passed (this may be a Unix timestamp).
  61
  62   Returns:
  63     A dict of process type names (Browser, Renderer, etc.) to ratios of cpu
  64     time used to total time elapsed.
  65   """
  66   cpu_usage = {}
  67   for process_type in cpu_stats:
  68     assert process_type in start_cpu_stats, 'Mismatching process types'
  69     # Skip any process_types that are empty.
  70     if (not cpu_stats[process_type]) or (not start_cpu_stats[process_type]):
  71       continue
  72     cpu_process_time = (cpu_stats[process_type]['CpuProcessTime'] -
  73                         start_cpu_stats[process_type]['CpuProcessTime'])
  74     total_time = (cpu_stats[process_type]['TotalTime'] -
  75                   start_cpu_stats[process_type]['TotalTime'])
  76     # Fix overflow for 32-bit jiffie counter, 64-bit counter will not overflow.
  77     # Linux kernel starts with a value close to an overflow, so correction is
  78     # necessary.
  79     if total_time < 0:
  80       total_time += 2**32
  81     # Assert that the arguments were given in the correct order.
  82     assert total_time > 0 and total_time < 2**31, (
  83         'Expected total_time > 0, was: %d' % total_time)
  84     cpu_usage[process_type] = float(cpu_process_time) / total_time
  85   return cpu_usage
  86