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Investigate too low values in devtools timeline
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Description

Multiple times the devtools.timeline metrics has been just too low, something must be wrong somewhere:

Screen Shot 2018-01-27 at 9.22.38 PM.png (1×834 px, 118 KB)

Screen Shot 2018-01-27 at 9.22.19 PM.png (624×1 px, 145 KB)

The problem can be:

  • The trace log from Chrome
  • The devtools.timeline package that somehow get the metrics wrong
  • The code I added somehow get the metrics wrong

To debug it, we need to store the trace log on the server, the easiest is just to store the latest version on the local server. Let me try that on Monday.

Event Timeline

Peter triaged this task as Medium priority.

Deployed the new parsing lib, hope that we will not see this there.

We still have the problem with the new trace-parser, so it is either a problem with the trace log itself or how we pick the value. I look into it when we store the trace log.

Screen Shot 2018-01-31 at 6.42.02 AM.png (920×820 px, 108 KB)

When I think of it, I think we have the same for our WebPageTest runs:

Grafana   WebPageTest.png (370×844 px, 40 KB)

Let me collect a trace log the next time it happens and create an upstream bug.

Found runs that produces the same bug with WebPageTest so I filed a upstream bug:
https://github.com/WPO-Foundation/webpagetest/issues/1100

But I guess the origin of the bug is in Chrome.

Hmm this could actually be T186101 that is the cause (=not the same as in WebPageTest).

Yep it is T186101 and upstream issue created.