We have support for a very limited async-integrated tracing profiler!
When starting a daemon with -tracing or using mina client start-tracing,
it will write *.trace files into its config directory. They can grow
quite fast, but for the most part they grow no faster than 5MB/minute.
Most of the integration tests (including full-test) support a MINA_TRACING
environment variable that specifies the directory the integration tests
will put their trace files in. If you leave it empty, no tracing will
occur.
Once you have a .trace file, it needs to be turned into JSON for the
Chrome trace-viewer to view. You can do this with src/app/trace-tool.
Using it is simple if you have Rust installed: cd src/app/trace-tool; cargo run --release /path/to/1234.trace > trace.json.
Then you can load the file from chrome://tracing.
Each row correponds to a "task" as created by either O1trace.trace_task or
O1trace.trace_recurring_task. A recurring task starts with R&. Internally
it works by doing one trace_task per call, and the trace-tool knows how
to collapse them all into one row.
In the screenshot, the top green bar represents the root of a recurring task.
The bars underneath it each correspond to a measure call - which can be nested.
The very thin lines correspond to a trace_event call - these are labeled instantaneous
events. Think of like a printf that shows up in the trace.