Slow rendering is not reported correctly on tvOS

[mkj-is]

Description

We received around 150x higher values for Slow rendering in our app on tvOS (~60 %) than iOS (<1 %). This led us to an investigation why this could be happening.

• Most iOS devices have 60 Hz screen, so this works almost correctly on iOS. Except for devices with ProMotion screens with refresh rates from 10-120 Hz. If a device is appropriately rendering in slower refresh rates it will be reported as a slow rendering, which is undesirable.
• Apple TVs are connected to different TVs and the default setting for refresh rate can be different in some parts of the world. (In Central Europe it is usually 50 Hz). If the default TV setting or user setting is 50 Hz or less then slow rendering will be reported. This seems undesirable too.

I am not sure what would be the best solution to improve this metric. I think the least what can be done is to mention this in the documentation.

Reproducing the issue

Set your TV to slow refresh rate and check slow rendering values.

Firebase SDK Version

9.4.1

Xcode Version

13.4.1

Installation Method

CocoaPods

Firebase Product(s)

Performance

Targeted Platforms

iOS, tvOS

Relevant Log Output

No response

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If using CocoaPods, the project's Podfile.lock

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[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[morganchen12]

For tvOS, we can programmatically check the attached TV's refresh rate and update our definition of slow frames accordingly. For variable refresh rate displays like ProMotion this becomes much harder, Perf folks see this doc for more details.

[jfcong]

Thanks for raising this @mkj-is. The Perf SDK has the assumption about the device having a refresh rate of 60fps when calculating slow and frozen frames, and I will definitely be adding this to our documentation. I've also raised this with the eng team and we will see when we can prioritize looking into this and making the screen traces metrics more accurate for devices with different refresh rate. This might not be something we can easily change so we will have to investigate more, but it's definitely on our radar now!

[mkj-is]

Thanks for acknowledging this issue. I get why this might be hard to implement from your side, it would interfere with historic data when updating Firebase. But with more and more ProMotion devices the importance of this might be larger in the future.