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 import logging
   6
   7 from telemetry.value import scalar
   8
   9 from metrics import Metric
  10
  11
  12 class CpuMetric(Metric):
  13   """Calulates CPU load over a span of time."""
  14
  15   def __init__(self, browser):
  16     super(CpuMetric, self).__init__()
  17     self._browser = browser
  18     self._start_cpu = None
  19     self._stop_cpu = None
  20
  21   def DidStartBrowser(self, browser):
  22     # Save the browser object so that cpu_stats can be accessed later.
  23     self._browser = browser
  24
  25   def Start(self, page, tab):
  26     if not self._browser.supports_cpu_metrics:
  27       logging.warning('CPU metrics not supported.')
  28       return
  29
  30     self._start_cpu = self._browser.cpu_stats
  31
  32   def Stop(self, page, tab):
  33     if not self._browser.supports_cpu_metrics:
  34       return
  35
  36     assert self._start_cpu, 'Must call Start() first'
  37     self._stop_cpu = self._browser.cpu_stats
  38
  39   # Optional argument trace_name is not in base class Metric.
  40   # pylint: disable=W0221
  41   def AddResults(self, tab, results, trace_name='cpu_utilization'):
  42     if not self._browser.supports_cpu_metrics:
  43       return
  44
  45     assert self._stop_cpu, 'Must call Stop() first'
  46     cpu_stats = _SubtractCpuStats(self._stop_cpu, self._start_cpu)
  47
  48     # FIXME: Renderer process CPU times are impossible to compare correctly.
  49     # http://crbug.com/419786#c11
  50     if 'Renderer' in cpu_stats:
  51       del cpu_stats['Renderer']
  52
  53     # Add a result for each process type.
  54     for process_type in cpu_stats:
  55       trace_name_for_process = '%s_%s' % (trace_name, process_type.lower())
  56       cpu_percent = 100 * cpu_stats[process_type]
  57       results.AddValue(scalar.ScalarValue(
  58           results.current_page, 'cpu_utilization.%s' % trace_name_for_process,
  59           '%', cpu_percent, important=False))
  60
  61
  62 def _SubtractCpuStats(cpu_stats, start_cpu_stats):
  63   """Computes average cpu usage over a time period for different process types.
  64
  65   Each of the two cpu_stats arguments is a dict with the following format:
  66       {'Browser': {'CpuProcessTime': ..., 'TotalTime': ...},
  67        'Renderer': {'CpuProcessTime': ..., 'TotalTime': ...}
  68        'Gpu': {'CpuProcessTime': ..., 'TotalTime': ...}}
  69
  70   The 'CpuProcessTime' fields represent the number of seconds of CPU time
  71   spent in each process, and total time is the number of real seconds
  72   that have passed (this may be a Unix timestamp).
  73
  74   Returns:
  75     A dict of process type names (Browser, Renderer, etc.) to ratios of cpu
  76     time used to total time elapsed.
  77   """
  78   cpu_usage = {}
  79   for process_type in cpu_stats:
  80     assert process_type in start_cpu_stats, 'Mismatching process types'
  81     # Skip any process_types that are empty.
  82     if (not cpu_stats[process_type]) or (not start_cpu_stats[process_type]):
  83       continue
  84     cpu_process_time = (cpu_stats[process_type]['CpuProcessTime'] -
  85                         start_cpu_stats[process_type]['CpuProcessTime'])
  86     total_time = (cpu_stats[process_type]['TotalTime'] -
  87                   start_cpu_stats[process_type]['TotalTime'])
  88     # Fix overflow for 32-bit jiffie counter, 64-bit counter will not overflow.
  89     # Linux kernel starts with a value close to an overflow, so correction is
  90     # necessary.
  91     if total_time < 0:
  92       total_time += 2**32
  93     # Assert that the arguments were given in the correct order.
  94     assert total_time > 0 and total_time < 2**31, (
  95         'Expected total_time > 0, was: %d' % total_time)
  96     cpu_usage[process_type] = float(cpu_process_time) / total_time
  97   return cpu_usage
  98