Performance Bar: "Wall" mode is broken
The issue
The "wall" mode of Stackprof in Performance bar is missing data:
We don't see any stack frames after Puma worker startup.
How to replicate
Enable the performance bar as described in https://docs.gitlab.com/ee/administration/monitoring/performance/performance_bar.html
Click on the Flamegraph with mode: wall
.
Note that there are no frames after the worker startup.
Similar problems
We observe a similar issue with our Google Cloud profiler on staging (it also uses StackProf):
Actions
We need to investigate. The wall mode is valuable for us, as Matthias mentioned:
One benefit of wall time sampling is that it acts more like a tracer since the gaps spent in IO would become visible
Ideas
There may be a potential connection with the Ruby 3 upgrade?