Flame Graphs

Talk I gave at Slovenia Ruby User Group meetup in May '16. What are flame graphs, how to read them, simple tutorial, practical example.

Further read:
- The Flame Graph: http://queue.acm.org/detail.cfm?id=2927301
- flamegraph gem: https://github.com/SamSaffron/flamegraph
- rack-mini-profiler: https://github.com/MiniProfiler/rack-mini-profiler
- ruby-prof-flamegraph: https://github.com/oozou/ruby-prof-flamegraph

Transcript

1. FLAME GRAPHS
2. WHY AND WHAT • How SW is consuming CPU • DTrace is verbose and unreadable • Brendan Gregg • combine stack traces with common paths
5. FLAME GRAPHS EXPLAINED • each box represents a function (a merged stack frame) • y-axis (vertical) shows stack depth • top function led directly to the profiling event • everything beneath it is ancestry (explains why) • x-axis (horizontal) shows the sample sorted alphabetically • box width shows the total time it was on-CPU
6. LOOKS
7. TUTORIAL Q: Which function is on CPU the most?
8. TUTORIAL A: f() top edge shows who is on CPU directly
9. TUTORIAL Q: Why is f() on CPU?
10. TUTORIAL A: a() → b() → c() → e() → f() f() was called by e(), e() was called by c(),…
11. TUTORIAL Q: How does b() compare to g()?
12. TUTORIAL A: b() looks like it is running (present) about 10 times more often than g()
13. TUTORIAL Q: Why are we running f()?
14. TUTORIAL A: code path branches can reveal key functions:
 a() choose the b() path
 c() choose the e() path look for branches
15. REAL WORLD EXAMPLE • Sam Saffron • gem 'flamegraph' Flamegraph.generate(filename) do # your work here end
16. 1.083 (± 0.0%) i/s - 33.000 in 30.861265s ORIGINAL
17. 8.368 (±12.0%) i/s - 244.000 in 30.037836s | 7.5x improvement CACHE KRAMDOWN
18. 10.140 (± 9.9%) i/s - 292.000 in 30.025553s | 9.4x improvement MEMOIZATION & CO.
19. FURTHER READ • The Flame Graph: http://queue.acm.org/ detail.cfm?id=2927301 • flamegraph gem: https://github.com/SamSaffron/ flamegraph • rack-mini-profiler: https://github.com/ MiniProfiler/rack-mini-profiler • ruby-prof-flamegraph: https://github.com/oozou/ ruby-prof-flamegraph