Trace capture: include JS stacks, exclude netlog

[paulirish]

We can afford to include the JS stacks now, which allows us to start attributing cost at a function level. Moreover, when you view a LH trace in timeline, having the stacks tells fleshes out the flame chart inside of "Evaluate Script" etc.

I've looked at the trace size overhead of various categories and we can trade netlog for cpu_profiler right now for free.

I profiled the load of theverge.com in three modes:

1. hi-res sampling (cpu_profiler & cpu_profiler.hires)
2. lo-res sampling (cpu_profiler)
3. no sampling (no cpu_profiler at all)

full details: https://docs.google.com/spreadsheets/d/1T_i2ikSWMH13YzqnKPfrRGjTXrs-C-98jj6x8sipfu0/edit#gid=2071721736&vpid=A6

You can see the size overhead of netlog (which we added randomly without a clear usecase). Flipping that off and turning on cpu_profiler makes sense and shouldn't add much bytesize for general pageload traces.

I've also added latencyInfo which provides the "interaction" part of timeline, aka the "MouseUp" etc details. This has totally negligible filesize (or runtime) overhead.

[brendankenny]

does enabling cpu_profiler.hires affect the other categories or were the differences in the other categories just from expected variance across multiple runs?

[paulirish]

does enabling cpu_profiler.hires affect the other categories or were the differences in the other categories just from expected variance across multiple runs?

doesn't affect the others. yeah that's just variance from multiple runs.

[brendankenny]

🍬

[wardpeet]

I get this error when running npm start https://airhorner.com

I think we had this issue somewhere else as well, trying to find it

Running on canary 57

Lighthouse CLI Launching Chrome... +0ms
  ChromeLauncher Waiting for browser. +128ms
  ChromeLauncher Waiting for browser... +1ms
  ChromeLauncher Waiting for browser..... +510ms
  ChromeLauncher Waiting for browser.....✓ +16ms
  status Initializing… +1s
  status Loading page & waiting for onload +377ms URL, HTTPS, Viewport, ThemeColor, Manifest, Accessibility, ContentWidth
  statusEnd Loading page & waiting for onload +2s
  status Retrieving trace +1ms
  status Disconnecting from browser... +68ms
  ChromeLauncher Killing all Chrome Instances +2ms
Runtime error encountered: SyntaxError: Unexpected number in JSON at position 82724
    at Object.parse (native)
    at onChunkRead (/Volumes/MAC_EXTRA/Projects/tmp/lighthouse/lighthouse-core/gather/driver.js:549:31)
SyntaxError: Unexpected number in JSON at position 82724
    at Object.parse (native)
    at onChunkRead (/Volumes/MAC_EXTRA/Projects/tmp/lighthouse/lighthouse-core/gather/driver.js:549:31)

[paulirish]

Yup. Looks like the startTime in the trace for cpu_profiler is using locale numbers, which naturally breaks the JSON.parse()

[a1ph]

Oh, indeed. I'll fix that.

[a1ph]

https://bugs.chromium.org/p/v8/issues/detail?id=5820