pprof-rs VS profiler

On top of others' specific recommendations, don't forget to profile! Tools like perf on Linux and pprof within Rust will tell you which functions are taking the most time.

https://github.com/tikv/pprof-rs: Seems to work nicely per se, but I cant seem to find any useful information in the flamegraph for my setting. I see mostly functions in std::thread but cant find the time it costs to render stuff or to do the actual computations which should be the most time consuming things. Not sure whether this is necessarily something wrong with pprof-rs, maybe I'm just bad at finding stuff in the flamegraph svg or bevys ECS is making this hard.

Have you looked into using pprof?

The library doesn't actually do any profiling (The profiler for Rust is pprof-rs: https://github.com/tikv/pprof-rs) but it's goal is to manage data returned by profilers (abstracted behind a Backend) and send this data to a Pyroscope Server (or exported to flamegraph, though this is being implemented in the commandline application).

The libunwind part is actually not related to overhead, this is just a nuance of the way that pprof-rs unwinds stack traces.

Probably your best bet is to use the Firefox Profiler once it starts hogging the CPU to try to see what it's doing. I'd be happy to take a look at the result although I don't have a lot of experience at diagnosing performance problems; hopefully the profile will make it obvious what's going on.

I tried using the https://profiler.firefox.com/ and running with:

You can try to reproduce while taking a profile using the Firefox profiler, then share it in the #perf:mozilla.org room on Mozilla's Matrix instance.

Run a profiling session for ~30 sec when you notice something is running slower than you expect, see https://profiler.firefox.com/. Share results here if you want help interpreting them.

Next time, send a SIGABRT to the main process (kill -6 $(pidof firefox)) and use the resulting backtrace (you will find a link to the crash report in about:crashes) to file a bug. A performance profile could be useful, but you'll need to know first what to capture. This seems like a graphics issue, so try the Graphics preset. Share a link to your report.

https://profiler.firefox.com will be useful if you can capture and share it to developers.

If you can reproduce it in safe mode and a clean profile, capture a performance profile using the clean profile while trying to load a problematic webpage, don't remove any information from it, and share it here (although it's typically not easy for users to analyse them), or file a bug with it attached.

Next time, capture a performance profile using the Graphics preset, and kill the browser by entering kill -6 $(pidof firefox) in a shell. This will create a bug report (unless debian disables the crash reporter) that would indicate where Firefox is stuck at. You might need to use an official build to get useful results.