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Add flutter frame identifier to timeline events on UI and Raster threads #80735
Description
In DevTools, we need a way to connect Flutter.Frame events (sent here) to their corresponding timeline events on the UI and Raster threads. This is a requirement in order to make the DevTools timeline show live frame data.
We cannot connect a Flutter.Frame event to its corresponding timeline events by timestamp because the two data sources use different clocks. From @iskakaushik:
Based on some initial observations, there doesn't seem to be an easy way to convert between Dart Timeline and Flutter Clocks. For example, on iOS, Dart timeline seems to use "mach_absolute_time" which doesn't increment when the system is asleep, whereas in Flutter we use "std::chrono::steady_clock()" which is independent of the system uptime.
If we could add metadata to the root UI thread and root Raster thread event that would allow us to associate those two timeline events with a Flutter.Frame event, that would work. Perhaps adding an arg "frameNumber" that matches the "number" field from Flutter.Frame events.
Activity
jonahwilliams commentedon Apr 19, 2021
@kenzieschmoll is there any reason not to go with the frame-janks-are-errors design of have the framework plumb through the frame identifier? If not, I can wire that up fairly quickly....
kenzieschmoll commentedon Apr 19, 2021
would this result in both the UI root event and the Raster root event having the identifier in their trace events?
jonahwilliams commentedon Apr 19, 2021
Yes, the information should be available in the engine when we write the traces. I didn't wire that up in the prototype but can't imagine it would be that hard (famous last words)
kenzieschmoll commentedon Apr 19, 2021
Then that sounds like exactly what we need.
iskakaushik commentedon Apr 21, 2021
Capturing the offline discussion with @jonahwilliams:
I like the idea of having a frame identifier that is associated with trace events. Given that engine triggers the frame build and raster process, it would be best if engine does the creation and managing lifecycle of the said frame identifier.
Next steps are for Jonah and I to iterate on flutter-team-archive/engine#25662.
jonahwilliams commentedon Apr 30, 2021
Another use for this would be flutter/devtools#2943
kenzieschmoll commentedon Apr 30, 2021
To meet this use case, the starting frame number would need to be consistent (0-based or 1-based) so we can identify the first frame for an app run.
Streamline frame timings recording
Streamline frame timings recording
Streamline frame timings recording
Streamline frame timings recording
Streamline frame timings recording
Streamline frame timings recording
Streamline frame timings recording
iskakaushik commentedon May 12, 2021
flutter-team-archive/engine#25892 and flutter-team-archive/engine#26021 partially address the issue. Per my conversations with @jonahwilliams and @kenzieschmoll , the next AIs are:
frame_numberas a trace event argument in animator and rasterizer events.frame_numberfield via the service protocol FrameTimings APIs.Thanks and let me know if I'm missing something here.
kenzieschmoll commentedon May 24, 2021
Interestingly, the frame numbers don't seem to be incrementing by 1. In this example they are increasing by 3 - is that expected? @iskakaushik @jonahwilliams
jonahwilliams commentedon May 24, 2021
That is surprising to me at least :)
iskakaushik commentedon Jun 1, 2021
I saw it alternating each time, 1, 3, 5...
This PR should fix it: flutter-team-archive/engine#26513. At least locally after this change I'm seeing every number appear.
zanderso commentedon Jul 8, 2021
What is left to do for this?
kenzieschmoll commentedon Jul 12, 2021
I think this is complete.
github-actions commentedon Jul 30, 2021
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