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Timeline doesn't show descheduled time #3454
Description
Activity
Duplicate issue: #778
From a linked issue, developer reported a randomly long timeline event. In devtools, it was impossible to tell that this was due to descheduling, whereas in observatory it was obvious:
Particularly bad because the descheduled time was very long (almost 80ms).
Which part of this is thread descheduled time? Is it the more opaque portion of the timeline event?
The more opaque part is scheduled time - the more transparent part is descheduled.
One missing part here that perfetto has is showing you which parts of the event were descheduled, but I don't think we get that in the JSON format that the VM emits.
Oh man if we knew which part was descheduled that would be fantastic.
Perfetto/systrace can show that on Android.
@derekxu16 do you know if thread descheduling information is something that we can get (or something that we already have access to) with the perfetto recorder in the VM?
This functionality is not part of Observatory anymore either, because we stopped recording the "scheduled time" of events in dart-lang/sdk@08634ec for performance reasons.
As noted in the discussion, the Dart VM stopped recording and emitting scheduled time for timeline events (see dart-lang/sdk@08634ec) for performance reasons, and this functionality was also removed from Observatory. Because the underlying VM no longer provides thread scheduling data to DevTools, this cannot be supported in the DevTools timeline.
If there is more work to do here, please let us know by filing a new issue with up to date information. Thanks!
Sometimes, a thread spends 15ms of wall-clock time doing something, but only 1ms of CPU time. This represents 14ms where the CPU was busy doing something else. Other timeline viewers typically show this as a bar with a length of 15ms but where the trailing 14ms of the bar are partly faded out to indicate that the thread was descheduled.