LCA: Updates on the X Window System [LWN.net]

LCA: Updates on the X Window System

Posted Jan 26, 2007 2:23 UTC (Fri) by pimlott (guest, #1535)
Parent article: LCA: Updates on the X Window System

Keith noted that the policy of splitting the X drivers from the core server has not worked as well as they would have liked.

Can someone confirm: This is not referring to the recent modularization effort, but the stable ABI introduced with XFree86 4, right?

There is a lot of interest in supporting multiple, simultaneous X sessions on the same screen without using Linux virtual terminals; the goal here is to enable fast switching between user accounts.

What's wrong with using Linux virtual terminals? We've had fast user switching since day one!

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LCA: Updates on the X Window System

Posted Jan 26, 2007 6:03 UTC (Fri) by bronson (subscriber, #4806) [Link]

Because it's not fast. On most hardware, it takes many seconds of blackness for the graphics card to reset and the monitor to sync back up. Users do not like this at all. The blank screen and flickering tends to scare them. Just ask my girlfriend; she uses my account because she really doesn't like the couple seconds it takes to switch.

Go figure.

LCA: Updates on the X Window System

Posted Jan 26, 2007 17:07 UTC (Fri) by pimlott (guest, #1535) [Link]

The obvious follow-up: Why isn't it fast? If video modes are set in the kernel (as seems the plan), in the common case where the mode is the same in the old and new virtual terminals, no reset should be necessary. But I'm a graphics ignoramus, so I may be missing something.

LCA: Updates on the X Window System

Posted Jan 26, 2007 18:46 UTC (Fri) by bronson (subscriber, #4806) [Link]

When video modes are set in the kernel, it will be as you say.

Until then, it is up to the process to set up the card. How can the news process know what mode the card is currently in? Even if it COULD reliably read back the mode settings (and on most hardware you can't), it would also have to see if the framebuffer is obscured by a video surface or GL surface, or if it's rotated 90 degrees, or... It amounts to a ton of code.

So, until it's all in the kernel (2 years at least, maybe more, IMo) it's safest just to reset and start from scratch.