Why Is Moblin's X.Org Stack Faster Than In Ubuntu?

Canonical's Scott James Remnant recently set out to explore why X.Org started up so much faster on Moblin than on Ubuntu (particularly, the latest 9.04 development code). On an Atom-based netbook (the Dell Mini 9) he found it took Ubuntu's X Server about four seconds to start before the session manager was called. With Moblin on the same hardware it took just about a second and a half.

Scott began analyzing the X Server patch-set for Moblin, that included enabling UXA acceleration by default, avoiding duplicated saved hardware states, reducing the driver boot-time, and disabling other operations. However, Ubuntu already incorporated all of these patches besides using UXA acceleration. Ubuntu's X Server also has a few extra patches, but those didn't seem to impact the performance.

After that, Scott came to no conclusions, but has now thrown the ropes to the principal X maintainer at Canonical (Bryce Harrington) and their technical leader (Matt Zimmerman). His mailing list message with Bootchart results can be found on ubuntu-devel. Hopefully by Ubuntu 9.10 (the Karmic Koala) we will see an X Server start-up time closer to Moblin, but that means cutting the time in at least half. Beyond just the X Server being speedier, Moblin V2 Core Alpha boots super fast.

Remnant is also looking at sreadahead vs. readahead performance for improving Ubuntu's boot performance.