All graphs for this bug:
  https://chromeperf.appspot.com/group_report?bug_id=809503

(For debugging:) Original alerts at time of bug-filing:
  https://chromeperf.appspot.com/group_report?sid=db51288e666bdc11df4f8d8f2b60c3a1edd2e9ed0ca58241ab1a021491cd9438


Bot(s) for this bug's original alert(s):

chromium-rel-mac-retina

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/16ed7f31840000

📍 Couldn't reproduce a difference.
https://pinpoint-dot-chromeperf.appspot.com/job/16ed7f31840000

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/14ae54c2440000

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/12d66aac440000

This bisected money.cnn which doesn't have a very clear jump; trying to bisect some of the other pages.

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/12d66aac440000

Re-record loading.desktop story set by ksakamoto@chromium.org
https://chromium.googlesource.com/chromium/src/+/ea8b932d3e0df99e89dc606dc35335d10e414c94

Understanding performance regressions:
  http://g.co/ChromePerformanceRegressions

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/14ae54c2440000

tracing: TracingController -> Coordinator by chiniforooshan@chromium.org
https://chromium.googlesource.com/chromium/src/+/c77b44ebb53886e039c8471548c2050cceceda59

Understanding performance regressions:
  http://g.co/ChromePerformanceRegressions

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/12500ac9440000

1. Some of the regressions associated with this bug happened well after my CL, e.g. cpuTimeToFirstMeaningfulPaint_avg/cold/QQ.

2. It looks like my CL caused some of the stories to not produce any data. For example, there is no data for cpuTimeToFirstMeaningfulPaint_avg/cold/FC2Blog since Oct 10th. On Feb 5th we suddenly started to see data again.

So, I think we are seeing probably 2 independent issues here. For 1., I started another bisect to see if we can find the culprit. For 2., I see the following error in the pinpoint job:

Traceback (most recent call last):
  File "/base/data/home/apps/s~chromeperf/pinpoint:dev-dtu-bd2b366c.408074162383212776/dashboard/pinpoint/models/quest/execution.py", line 99, in Poll
    self._Poll()
  File "/base/data/home/apps/s~chromeperf/pinpoint:dev-dtu-bd2b366c.408074162383212776/dashboard/pinpoint/models/quest/read_value.py", line 240, in _Poll
    raise ReadValueError('Could not find values matching: %s' % name)
ReadValueError: Could not find values matching: histogram: timeToFirstMeaningfulPaint tir_label: cold story: FC2Blog

dtu@ or simonhatch@, could you please help me understand what the error means? Thank you!

It means that after parsing the results of the test, it couldn't find the specified metric. It needs to find a histogram with name"timeToFirstMeaningfulPaint" with 2 diagnostics that match the tir_label and story. That could be down to a few reasons, the test is possibly broken and not generating it, or it's possible that it's there but we're not finding it for whatever reason.

So looking a bit more closely, the histograms are there but they contain no values. We should update the error, but it looks like the test wasn't generating any values in that range.

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/15d96379440000

📍 Found a significant difference after 1 commit.
https://pinpoint-dot-chromeperf.appspot.com/job/12500ac9440000

Re-record loading.desktop story set by ksakamoto@chromium.org
https://chromium.googlesource.com/chromium/src/+/ea8b932d3e0df99e89dc606dc35335d10e414c94

Understanding performance regressions:
  http://g.co/ChromePerformanceRegressions

😿 Pinpoint job stopped with an error.
https://pinpoint-dot-chromeperf.appspot.com/job/15d96379440000

The regression could be due to the story set re-recording.
https://chromium.googlesource.com/chromium/src/+/ea8b932d3e0df99e89dc606dc35335d10e414c94

The issue loading stories not producing metrics is tracked at  Bug 809833 .

📍 Pinpoint job started.
https://pinpoint-dot-chromeperf.appspot.com/job/148c9907440000