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.
5 from metrics import Metric
6 from telemetry.value import scalar
9 class CpuMetric(Metric):
10 """Calulates CPU load over a span of time."""
12 def __init__(self, browser):
13 super(CpuMetric, self).__init__()
15 self._browser = browser
16 self._start_cpu = None
18 def DidStartBrowser(self, browser):
19 # Save the browser object so that cpu_stats can be accessed later.
20 self._browser = browser
22 def Start(self, page, tab):
23 self._start_cpu = self._browser.cpu_stats
25 def Stop(self, page, tab):
26 assert self._start_cpu, 'Must call Start() first'
27 self._results = _SubtractCpuStats(self._browser.cpu_stats, self._start_cpu)
29 # Optional argument trace_name is not in base class Metric.
30 # pylint: disable=W0221
31 def AddResults(self, tab, results, trace_name='cpu_utilization'):
32 assert self._results, 'Must call Stop() first'
33 # Add a result for each process type.
34 for process_type in self._results:
35 trace_name_for_process = '%s_%s' % (trace_name, process_type.lower())
36 cpu_percent = 100 * self._results[process_type]
37 results.AddValue(scalar.ScalarValue(
38 results.current_page, 'cpu_utilization.%s' % trace_name_for_process,
39 '%', cpu_percent, important=False))
42 def _SubtractCpuStats(cpu_stats, start_cpu_stats):
43 """Computes average cpu usage over a time period for different process types.
45 Each of the two cpu_stats arguments is a dict with the following format:
46 {'Browser': {'CpuProcessTime': ..., 'TotalTime': ...},
47 'Renderer': {'CpuProcessTime': ..., 'TotalTime': ...}
48 'Gpu': {'CpuProcessTime': ..., 'TotalTime': ...}}
50 The 'CpuProcessTime' fields represent the number of seconds of CPU time
51 spent in each process, and total time is the number of real seconds
52 that have passed (this may be a Unix timestamp).
55 A dict of process type names (Browser, Renderer, etc.) to ratios of cpu
56 time used to total time elapsed.
59 for process_type in cpu_stats:
60 assert process_type in start_cpu_stats, 'Mismatching process types'
61 # Skip any process_types that are empty.
62 if (not cpu_stats[process_type]) or (not start_cpu_stats[process_type]):
64 cpu_process_time = (cpu_stats[process_type]['CpuProcessTime'] -
65 start_cpu_stats[process_type]['CpuProcessTime'])
66 total_time = (cpu_stats[process_type]['TotalTime'] -
67 start_cpu_stats[process_type]['TotalTime'])
68 assert total_time > 0, 'Expected total_time > 0, was: %d' % total_time
69 cpu_usage[process_type] = float(cpu_process_time) / total_time