Debug Mobile Rendering Jank

Context

Mobile UI performance issues are common in consumer apps such as Instagram, especially on animation-heavy screens. Interviewers ask this to evaluate whether you can debug performance systematically instead of guessing.

Core Question

A mobile screen feels janky during scroll or animation. Walk through how you would diagnose and fix it.

Address these points:

1. How do you confirm the issue and define a measurable performance target such as frame time or dropped frames?
2. What profiling steps do you use to determine whether the bottleneck is on the main thread, render thread, GPU, layout, image decoding, or memory/GC?
3. What fixes would you apply for common causes, and how would you verify that the fix actually improved performance?

Scope Guidance

The interviewer expects a structured debugging process, not platform-specific trivia. You should explain the rendering pipeline at a practical level, describe the signals you would inspect in profiling tools, and connect likely symptoms to targeted fixes.