This document discusses the Go execution tracer tool. It provides an overview of the tool, how it can be used to collect trace data, and how the trace data can be analyzed. Specifically, it explains that the tracer instruments the Go runtime to capture events like goroutine creation and scheduling with nanosecond precision. It provides examples of using the tracer to optimize concurrency in applications and debug strange behaviors. The document concludes by noting that while the tracer is useful for understanding concurrency, it lacks documentation, providing an opportunity for community contributions.

1. Go execution tracer
Gophercon Brazil 2017
André Carvalho

2. $ whoami
• Developer @ globo.com /
tsuru
• Interested in all things
performance, tracing and
systems programming
• @andresantostc
• https://andrestc.com

3. Agenda
• The tool basics
• What is the Go execution tracer
• How to collect trace data
• How to analyze trace data
• Using the tracer
• to improve working code
• to investigate a strange behavior

4. Go execution tracer
• Gives insight into the execution of a Go program
• What are my goroutines doing when not in CPU?
• Instruments the go runtime
• Captures events in nanosecond precision
• Data is not aggregated/sampled!
• Available since go 1.5

5. Go execution tracer
• Events
• Goroutines creation/start/end/block/unblock
• Network
• Syscalls
• Memory allocation
• Garbage collection

6. Collecting traces
• Three ways to collect traces
• trace.Start / trace.Stop
• go test -trace=trace.out
• debug/pprof/trace handler

7. Collecting traces
• Writes the tracing output to
os.Stderr
• go run main.go 2> trace.out
• go tool trace trace.out

8. Trace

9. View Trace
1. Timeline
2. Heap usage
3. goroutines
1
2
3
4
5
4. OS threads
5. Virtual Processors
6. goroutine + events
6

10. View Trace
Selecting a goroutine

11. View Trace
Selecting an event

12. Tracing web applications
https://github.com/andrestc/go-tracing/tree/master/07-web

13. Using the tracer to
improve working code

14. Mandelbrot
CPU intensive calculations to
figure out each pixel’s color
https://github.com/campoy/
mandelbrot/

15. Pixel

16. Sequential

17. Sequential

18. One goroutine per pixel

19. One goroutine per pixel

20. One goroutine per pixel

21. One goroutine per column

23. Debugging a strange
test behavior

24. Planb
• github.com/tsuru/planb
• reverse proxy based of hipache
• One of tsuru’s key components
• Used extensively on globo.com

25. Planb
Planb
Host: app.cloud.com
Backend
Backend
Backend

28. Let’s trace it!

32. https://github.com/golang/go/issues/21204

33. Workaround
https://github.com/tsuru/planb/pull/35

34. Conclusions
• Go execution tracer helps understand concurrency
• Complements other tools (eg memory/cpu
profile)
• Not much documentation available
• Opportunity for contributions

35. Reference
• Using the go tracer to speed up fractal rendering
• Just for func #22
• Go Execution Tracer (Design Doc)

36. Slides and notes in english
will be available at
https://andrestc.com
Obrigado!