Back in August I talked about the lack of benchmarks or performance tools for CSS. In the meantime, the fine folk we call browser makers have been working hard on new developer tools to do just that: measure CSS performance. First the Opera team showed off their upcoming style profiler, and now the WebKittens are tinkering on a CSS selector profiler too.
One of the features of these tools is to calculate how long your selectors take and then show a list of the worst offenders. But as you can see from the screenshots, and as noted by Pavel Feldman:
I can see selector matching taking single digit milliseconds. I know from the timeline panel that layout takes hundres of milliseconds or even seconds.
So the relevance of this information may be rather marginal. Perhaps more interesting then is the fact that the Opera Dragonfly style profiler shows the exact moment and location of paint events and layout reflows. Definitely some exciting developments to keep an eye on!