A brief overview of profiling Node.js and writing code for the V8 runtime.

1. Run Node Run
Fine-tuning JavaScript for
the V8 Runtime
@kevinswiber kswiber@gmail.com

2. Agenda
• Benchmarking
• V8 JavaScript Tips and Tricks
• Inside Crankshaft
• Profiling Node

3. From 365 to 5,000 requests per
second.

4. This shit works. Swears it.

5. Note: This is complex, but you’ll sleep
better at night.

6. If you can sleep at all.

7. This is about speed.

8. Speed is addictive.

9. Benchmarking

10. HTTP

11. $ ab -n1000 –c100 –k http://127.0.0.1/

12. $ siege –r100 –c100 -b http://127.0.0.1/

13. JMeter

14. ab output
Concurrency Level: 100
Time taken for tests: 8.680 seconds
Requests per second: 11521.27 [#/sec] (mean)
Time per request: 8.680 [ms] (mean)
Time per request: 0.087 [ms] (mean,
across all concurrent requests)

15. Non-HTTP

16. var maxRuns = 1000;
var start = Date.now();
for (var i = 0; i < maxRuns; i++) {
// do stuff...
}
var end = Date.now();
var elapsed = end – start;
var timePerRun = elapsed / maxRuns;
console.log(elapsed + ‘ ms’);
console.log(timePerRun + ‘ ms/run’

17. Faster!

18. Hidden Classes
function Point(x, y) {
this.x = x;
this.y = y;
}
var p1 = new Point(1, 2);
var p2 = new Point(3, 4);

19. Hidden Classes
function Point(x, y) {
this.x = x;
this.y = y;
}
var p1 = new Point(1, 2);
var p2 = new Point(3, 4);
p2.z = 9; // ohnoes!!

20. Dictionary Mode
function takeOrder(row) {
var order = {
food: row.get(‘food’),
quantity: row.get(‘qty’);
};
process(order);
}

21. Dictionary Mode
function takeOrder(row) {
var order = {
food: row.get(‘food’),
quantity: row.get(‘qty’);
};
process(order);
}
// ohnoes!!!
for(var i = 0; i < db.length; i++) {
takeOrder(db[i]);
}

22. Try-Catch
try {
// hot code
} catch(e) {
console.log(e);
}

23. Try-Catch
try {
process();
} catch(e) {
console.log(e);
}
function process() {
// hot code
}

24. Hot Code
• Don’t monkey-patch.
• Don’t mix types for the same property.
• Avoid dictionary mode.
• Set all properties in the constructor.
• Move high-performance code out of try-catch.
• If array.length < 65000, specify the size.

25. V8’s Crankshaft is Awesome

26. Base Compiler

27. Runtime Profiler

28. Optimizing Compiler

29. Deoptimization Support

30. JavaScript ->
Hydrogen ->
Lithium ->
(Native)

31. Profiling Node

32. $ node --prof server.js

33. Note: Your benchmark will be slower.

34. $ ls
server.js v8.log
$ export D8_PATH=~/node/src/deps/v8
$ ~/nvm/src/node-v0.8.18/deps/v8/tools/mac-
tick-processor > profile.log

35. [JavaScript]:
ticks total nonlib name
251 0.5% 0.5% LazyCompile:
*Socket.write net.js:465
[C++]:
ticks total nonlib name
48625 94.4% 94.4% ___psynch_rw_unlock
[GC]:
ticks total nonlib name
263 0.5%

36. c4milo/node-webkit-agent

37. $ cat server.js
var agent = require('webkit-devtools-agent');
// create server
console.log(process.pid)
$ node server.js
22341
$ kill –SIGUSR2 22341
$ open http://c4milo.github.com/node-webkit-
agent/21.0.1180.57/inspector.html?host=localhost:1337&page=0

38. More Profiling Options

39. --trace_opt
• Shows code optimizations.
• Good for spotting hot code.

40. --trace_deopt
• Shows code de-optimizations.
• Good for spotting type information changes in
hot code.

41. “If you ain’t first, you’re last!”

42. The plumbing should work like greased
lightning.

43. You can’t control everything.

44. Fail with grace.

45. Benchmark regularly.

46. Additional Resources
• Understanding V8
• Breaking the JavaScript Speed Limit
• V8 Internals
• Profiling Node Programs on Mac OS X
• Node Webkit Agent

47. Adios!
@kevinswiber kswiber@gmail.com