Peter Flynn - Performance Tuning Secrets

JSConf US 2013

29 May 2013

Peter Flynn (Adobe)

everything after the initial execution matters - CSS, repaint, etc


*- Dev tools timeline tricks console.time() < - custom timeline marker Remote debugging API, JSON API exposed over a socket connection Telemetry testing framework on top of debugging API (Google) Includes UI automation - scrolling API enabled to simulate scrolling accurately

page.json -> controller for automation

topcoat project (open source css framework) -> good example of telemetry usage github: topcoat/topcoat-server FPS meter / continuous page repainting are useful (google this) show paint rectangles & layer borders - show repainting

*- chrome://tracing close all tabs except one you’re testing alt + mousewheel zooms A + D - pan horizontally W + Z - zoom in/out

600FPS camera filming actions to measure before FPS meter was available!

VM Guts (V8)

Memory profiling CPU profiling Instrumented CPU Profiling - console.profile(name) console.profileEnd(name) console.time(‘label’); console.timeEnd(‘label’);

V8 Logging Analysis plot-timer-events -> close all chrome insts. launch chrome with flags, run scripts on log produced, get PNG file graph.

code kind - optimized? Not optimized? obv. want optimized code running –range=start,end to filter down Tick processor - * = optimized no * = not optimized

opt/deopt tracing

  • see where unoptimized code is running and why optimization was disabled

chrome –no-sandbox –js-flags=”–trace-opt-verbose –trace-deopt” “file://foo.html” > opt-log.txt

Things that might be more important than JS perf optimizing:

  1. Network IO performance is very important
    • performance.timing;
    • performance.webkitGetEntriesByType(‘resource’);
    • appearance of speed is often just as good as actual speed (async processes meaning the action doesn’t block while it completes gives impression of being fast even if it’s not that fast)
  2. Code might be good enough already
    • If the actual impact of your less than optimal performance is not perceivably worse, no point in killing yourself to get 80m ops per second versus 12m ops per second when 12m ops per second is faster than can be perceived by user, move on!
  3. Better use of time?
    • code cleanup / fixing bugs / documenting / etc



JSConf 2013

This is a quick summary of a talk I attended at JSConf 2013. You can see a list of all those I've summarized notes from here. There's also a General thoughts during JSConf 2013 post for all the non-talk bits and pieces.

There were 3 concurrent tracks at the conference, so only those I attended myself are summarized here. Other attendees have summarized some of the talks I didn't get to due to scheduling conflicts - you can find those at (James Long) and Toby Ho's github repo.