Fedora 17′s out-of-the-box plug and play USB multiseat is awesome for sharing one system with many users — but there’s a way to dramatically boost performance and scalability, by changing the Fedora defaults.
Fedora 17 continues to default to GNOME 3, which assumes the presence of powerful 3D hardware.
If that’s not the case (e.g. in a VM, or with Fedora 17′s new automatic USB multiseat functionality), then Fedora 17 defaults to llvmpipe based software 3D, which is software to make full use of your CPU to do all the work there.
That’s great on a fast CPU with multiple cores (Core i3 class and up), but it brings lesser processors to their knees. Users can unnecessarily perceive Linux as slow and unusable. On a USB multiseat system, where you don’t have a 3D GPU and so are using llvmpipe, the load can be unacceptable even for a single user on a Core 2 class system. But by going to GNOME 3 “fall back mode” (which depends less on 3D composting for eye candy), having 5-6 users even on a dual core Atom system is no problem. It’s a dramatic performance difference.
You can tell if Fedora 17 is running llvmpipe by opening “System Settings”, and then “Details”
Then click on the “Graphics” tab. If it shows a driver of Gallium on llvmpipe, and “Standard” experience, then you’re in this mode where you’ll see high CPU usage at all times (even when no graphics appear to be changing!) because of GNOME 3′s 3D effects.
How to boost performance
But by hitting the “Forced Fallback Mode” switch to on, you can drop the GNOME 3 UI, enormously reduce your CPU load, and get a user experience that’s closer to what people are used to (more GNOME 2 like — has a task bar, potential for desktop icons, etc.). Maybe they should have renamed the setting …
On a Fedora 17 system with a bunch of USB thin clients attached, you can gain a ton of performance by making this change. But you’ll likely want to make this change in dconf configuration (so it also applies to the login screens). For that, read the follow-up post on configuring all users for GNOME 3 fallback.