qgis/qgis-js

Initial high CPU load on Firefox

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#45 opened on Jun 27, 2024

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Description

When Firefox is loading the qgis-js WebAssembly module, one core is 100% busy for some time. This is likely something FF does internally when loading such a large .wasm module:

  • The high CPU load goes towards zero after some time (~4min on my machine). The website is still working/responsive after that and stays idle when doing more render calls
  • The same thing happens with the 0.0.3 version, see https://boardend.github.io/qgis-js-baseline/
  • The same thing happens if I just return 0 in the main function
  • This behavior was observed in FF on Ubuntu Wayland and X11, also on FF on Windows 11
  • FF profiler only shows that the PollWrapper is busy polling
  • Hard to judge, but it seems that other larger Qt projects show similar behavior, although not as extreme as in qgis-js:

Contributor guide

Research direction
Investigate why Firefox has high CPU load during WebAssembly module initialization. Use Firefox profiler to trace the PollWrapper activity and check if there's a way to reduce the initial load time or work around it.
Tech stack
typescriptcppwasm
Domain
performance
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitWebAssembly basicsFirefox profiler
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70