What Are Flame Graphs and How to Read Them - DevConTLV X

A talk I gave at DevConTLV X in November 2016

https://www.youtube.com/watch?v=lIo0cEhT-Js

Further read:
- The Flame Graph: http://queue.acm.org/detail.cfm?id=2927301
- Blazing Performance with Flame Graphs (video): https://www.usenix.org/conference/lisa13/technical-sessions/plenary/gregg
- 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. ! @mr_foto
2. COMING HERE
3. COMING HERE
4. COMING HERE
6. WHOIS @mr_foto # Software Developer $ Ruby Slovenia organizer % Long Distance Runner & Event Photographer ☕ Coffee Connoisseur ⌨ Keyboard Enthusiast ) Special
7. *FLAME GRAPHS*
8. WHY AND WHAT • Interactive visualization of stack traces • From beginners to experts • Can be used for many things • How SW is consuming CPU • Brendan Gregg
12. 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
14. SAMPLING • Time interval • Observe what’s going on • Which action caused current action • Real-world example
15. SAMPLING My Day Reading Emails
16. My Day Reading Emails Replying to Emails SAMPLING
17. My Day Writing Code SAMPLING
18. My Day Writing Code Writing Tests SAMPLING
19. My Day Writing Code Writing Tests Running Tests SAMPLING
20. My Day Writing Code Writing Tests Running Tests Fixing Tests SAMPLING
21. My Day Writing Code Running Tests SAMPLING
22. My Day Making Espresso SAMPLING
23. SAMPLING My Day Reading Emails
24. My Day Writing Code SAMPLING
25. My Day Writing Code Running Tests SAMPLING
26. My Day Reading Emails Replying to Emails SAMPLING
27. SAMPLING
28. GROUPING
29. GROUPING
30. GROUPING My Day Reading Emails Replying Writing Code ☕ Writing Tests Running Running Fix
31. MOAR EXPLAINING Function
32. MOAR EXPLAINING Stack Depth
33. MOAR EXPLAINING Stack Depth
34. MOAR EXPLAINING Ordered by Alphabet
35. MOAR EXPLAINING Total Time on CPU
36. Q&A Q: Which function is on CPU the most?
37. Q&A A: f() top edge shows what is on CPU directly
38. Q&A Q: Why is f() on CPU?
39. Q&A A: a() → b() → c() → e() → f() f() was called by e(), e() was called by c(),…
40. Q&A Q: How does b() compare to g()?
41. Q&A A: b() looks like it is running (present) about 10 times more often than g()
42. Q&A Q: Why are we running f()?
43. Q&A A: code path branches can reveal key functions:
 a() choose the b() path
 c() choose the e() path look for branches
44. FOR REAL
45. REAL WORLD EXAMPLE • Sam Saffron • gem 'flamegraph' Flamegraph.generate(filename) do # your work here end
46. 1.083 (± 0.0%) i/s - 33.000 in 30.861265s ORIGINAL
47. 8.368 (±12.0%) i/s - 244.000 in 30.037836s | 7.5x improvement CACHE KRAMDOWN
48. 10.140 (± 9.9%) i/s - 292.000 in 30.025553s | 9.4x improvement MEMOIZATION & CO.
49. NOW WHAT? • You’re here • Ask me • Ask someone smarter than me • Ask anyone else • Read/watch blog posts/videos
51. http://mr.si/
 @mr_foto THANK YOU http://rug.si/
 @RubySlovenia