BDConf: Guy Podjarny presents Performance Implication of Mobile Design

In Performance Implication of Mobile Design, Guy Podjarny (@guypod) discusses performance best practices for dedicated mobile sites and responsive designs. Performance Matters

Web users will typically wait about 2-3 seconds for a site to load. Research shows if the users can't load a page quickly, they'll abandon ship and head to the competition.
Mobile users have same expectations as desktop users. They want sites to load as fast if not faster than desktop sites.

Performance for Separate Sites

Dedicated mobile websites cause redirect problems, which are extremely costly for performance.
ESPN's dedicated mobile site redirect caused a delay of 1.3 second, and that's before any content begins to download
Javascript redirects are much slower than server-side redirects. Avoid using client-side redirects for mobile detection.
Redirects burn up the 2-3 second frame you have to gain a user. You've already lost them by the time the page actually starts to load.
Minimize redirects. Use HTTP redirects, not JS redirects. Cache HTTP Redirects on the CDN. HTTP 301 Redirects w/ a future Expiry.

Performance for Responsive Designs

Responsive sites typically download a lot more content than you need.
50%-90% of responsive sites had little to no performance savings on small screens than on large screens
Only 3% of responsive sites had a much smaller performance footprint on small screens than on large screens
Smashing Magazine has a rich sidebar with a lot of ads and content, and gets hidden for small screens. However, hidden content still gets downloaded.
Avoid using display: none; to hide content for smaller screens in responsive designs. The content still gets downloaded even though it's not being used.
Media queries don't prevent CSS downloads
Separate CSS files per media type typically get downloaded by browsers even if it doesn't meet the criteria.

Solutions

About 350K of roughly 520K of a page load is taken up by image downloads. One of the best things you can do is implement an adaptive image solution.
Your responsive site should match the file size of a dedicated mobile site. Build mobile first then enhance from there
Enhance via Javascript: Split your files by layout and resolution and progressively enhance based on the capabilities device
Measure your results. Without measuring all this is meaningless