Fix overflow for 32-bit jiffie counter on Android.

Fix overflow for 32-bit jiffie counter on Android.

BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=280635

[Victor Starodub, 2014-06-30 15:37:25]

This should fix some of the flakiness in telemetry_perf_unittests tests.

[Sami, 2014-06-30 15:52:26]

Thanks. Could you add a test too?

https://codereview.chromium.org/362533003/diff/1/tools/perf/metrics/cpu.py
File tools/perf/metrics/cpu.py (right):

https://codereview.chromium.org/362533003/diff/1/tools/perf/metrics/cpu.py#ne...
tools/perf/metrics/cpu.py:64: cpu_process_time =
(cpu_stats[process_type]['CpuProcessTime'] -
Does this field have the same problem? If so, maybe add a utility function that
does the subtraction with wraparound handling.

https://codereview.chromium.org/362533003/diff/1/tools/perf/metrics/cpu.py#ne...
tools/perf/metrics/cpu.py:69: # Android devices start with a value close to an
overflow, so correction is
Looks like this isn't really Android-specific but something that Linux does on
purpose, e.g.:

http://books.google.co.uk/books?id=h0lltXyJ8aIC&pg=PT250&lpg=PT250&dq=linux+j...

[Victor Starodub, 2014-06-30 16:15:02]

Thanks for review. Addressed comments. PTAL

https://codereview.chromium.org/362533003/diff/1/tools/perf/metrics/cpu.py
File tools/perf/metrics/cpu.py (right):

https://codereview.chromium.org/362533003/diff/1/tools/perf/metrics/cpu.py#ne...
tools/perf/metrics/cpu.py:64: cpu_process_time =
(cpu_stats[process_type]['CpuProcessTime'] -
On 2014/06/30 15:52:26, Sami wrote:
> Does this field have the same problem? If so, maybe add a utility function
that
> does the subtraction with wraparound handling.

No, this field is counted from the process start rather than system boot.

https://codereview.chromium.org/362533003/diff/1/tools/perf/metrics/cpu.py#ne...
tools/perf/metrics/cpu.py:69: # Android devices start with a value close to an
overflow, so correction is
Thanks. Fixed the comment

[Sami, 2014-06-30 16:25:16]

Thanks, lgtm.

https://codereview.chromium.org/362533003/diff/20001/tools/perf/metrics/cpu_u...
File tools/perf/metrics/cpu_unittest.py (right):

https://codereview.chromium.org/362533003/diff/20001/tools/perf/metrics/cpu_u...
tools/perf/metrics/cpu_unittest.py:34: # Test 32-bit overflow
nit: Add '.' at end.

[Victor Starodub, 2014-06-30 16:33:20]

The CQ bit was checked by starodub@google.com

[commit-bot: I haz the power, 2014-06-30 16:34:23]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/starodub@google.com/362533003/40001

[commit-bot: I haz the power, 2014-06-30 18:19:58]

Change committed as 280635