Unfortunately, I can't find the original perf file I get the flamegraph https://laladrik.xyz/img/pic.svg out of. However, I can create with a similar bunch of data and provide it soon.
Ok, now I remember what was the deal with Hotspot. It makes it possible to work with a flamegraph of mine. However, it takes almost half a minute to load my perf.data. However! I totally recommend Hotspot over my hack in case when you need to have a comprehensive view of the data. In particular, I love to see the off-CPU load, which my FlameGraphViewer doesn't show.
