1# Tracing 2 3Cloud Hypervisor has a basic tracing infrastructure, particularly focussed on 4the tracing of the initial VM setup. 5 6## Usage 7 8To enabling tracing, build with "tracing" feature. When compiled without the 9feature the tracing is compiled out. 10 11```bash 12cargo build --features "tracing" 13``` 14 15And then run Cloud Hypervisor as you wish, the trace will be written to the current directory as `cloud-hypervisor-<pid>.trace`. This is JSON file which you can inspect yourself. 16 17Alternatively you can use the provided script in 18`scripts/ch-trace-visualiser.py` to generate an SVG: 19 20For example: 21 22```bash 23scripts/ch-trace-visualiser.py cloud-hypervisor-39466.trace output.svg 24``` 25 26## Tracing in the codebase 27 28There are existing tracepoints in the code base; extra ones can be added for 29more detailed tracing. 30 31The `tracer::trace_scoped!()` macro is used to add the current existing scope 32appears as a block in the trace. Other than providing a useful name for the 33event nothing else is required from the developer. 34 35The `tracer::start()` and `tracer::end()` functions are already in place for 36generating traces of the boot. These can be relocated for focus tracing on a 37narrow part of the code base. 38 39A `tracer::trace_point!()` macro is also provided for an instantaneous trace 40point however this is neither in use in the code base currently nor is handled by 41the visualisation script due to the difficulty in representation in the SVG. 42 43
