Velocity online conference March 2011

March 15th, 2011. Tagged: performance, tools

Very rough notes from the event that just ended a few minutes ago

======== 1 ========

Tony Gentilcore (google) and Anderson Quach (MSFT) talked about the W3C working group and the specs for measuring performance:

  • Navigation timing spec - HTML document: DNS, handshakes, load events
  • Resource timing - how long JS, CSS, audio, video... take
  • User timing - interactions, such as clicking a link

Challenges: user security, privacy. Small overhead for browsers. Useful actionable data out.

Navigation timing:

  • window.performance - IE9 has no vendor prefix
  • otherwise window.webkitPerformance
  • FF4 probably shipping it too




Resource Timing spec - upcoming

foreach resource 

User Timing - upcoming

  >>> getMarks();
    'pagelet': 123456767

Stretch goals:

  • painting times
  • CPUs
  • visibility (is the page in a background tab)
  • allow real yealding setTimeout(0)
  • don't animate faster than the browser paints


======== 2 ========

Above the Fold Time: Measuring Web Page Performance Visually
Speaker: Jake Brutlag
Help from: Zoe Abrams, Pat Meenan (webpagetest) Google

What the user perception of page load timing is.

AFT (Above the Fold Timing) algo
AFT: When content above the fold stops changing and reaches its final state

Integrated in


  • AFT more representative than DOMContentLoaded or onload
  • onload - different in IE and FF, e.g. async scripts block onload or not


  • video capture
  • AFT cutoff time - upper bound, e.g. 45 sec for DSL
  • split pixels into static and dymanic (ads)
  • AFT = latest change of a static pixel

Magic number - 5 determined empirically
static pixels are those that change less than 5 times

Application - validate other metrics, cross-browser, visual
Limitation - lab only

{I ran on with AFT on.
The results are very close to onload, as expected.
It's a simple page. Results:

== break ==

Note from the sponsor StrangeLoop: a downloadable "State of the Union"
A study of top 2000 Alexa retail sites. Findings:

  1. 11.2 sec onload avg
  2. top 100 sites slower than the lower ranked
  3. those using CDNs are not faster
  4. failed to implement the basics - YSlow stuff

======== 3 ========

Next-gen YSlow
Betty Tso and Marcel Duran, Yahoo!

YSlow for Chrome last week
Not as accurate as Firefox cause headers, timing come from:
1. Crawl DOM
2. x-domain requests

Announcing YSlow bookmarklet version
for mobile and all other browsers to be released early april
YSlow now on Git?

Lots coming up, e.g:

  • Multi-language support
  • HAR-to-YSlow
  • YSlow export to JDrop

Bookmarket works like:
1. crawl DOM
2. Use YQL to get headers

     SELECT * FROM data.headers WHERE
      url IN ('http://...', 'http://...')

======== 4 ========

Visibility into Mobile Performance
Steve Souders, Google

Demo #1: framework connected to iPhone and Android apps
Mobile waterfalls
Demo #2: pcapperf
1. setup wifi hotspot on a pc/mac
2. tcpdump to capture .pcap file
3. upload .pcap to app
4. observe waterfall via pcap2har and harviewer
5. run pagespeed on the har
Demo #3: JDrop
Upload JSON so you can run something on mobile and view/analyze results in desktop's large screen
Works with the bookmarklet tools part of Steve's package of mobile meta-tool

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