On Monday 15 January 2001 13:15, Andrew Morton wrote:
> How serious an issue is the latency introduced by fbdevs?
Well, I like fbdev, as it's rock solid compared to svgalib, but the
retrace sync ioctl - as horrible implementation wise as it is
important for quality animation - is missing...
Anyway, I always use it for the consoles, as any text mode I managed
to set up looks quite horrible on high resolution 19"ers and 21"ers.
<off-topic>
BTW, does anyone know why X nearly always makes fbdev freak out, even
with the "X compatible" flag? Another mysterious thing is that
running some OpenGL app on Utah-GLX very often *fixes* the problem,
leaving a perfectly working fbdev display after shutting X down!
As to switching between X and fbdev consoles; at least on the G400, I
can't remember ever seing a freak out because of that. Rock solid.
</off-topic>
> I've taken a look at what's going on in there and it seems
> that it's fairly straightforward to fix (*). It definitely
> _needs_ fixing - it's putrid.
What needs fixind, more precisely?
One thing that's not in the mainstream kernel, and would have been
pretty problematic to fix is that retrace sync ioctl. That's probably
why it got kicked in the first place. It's still the only way to get
smooth animation, though... :-(
> The one drawback of the approach I'm thinking about is that
> kernel printk's from interrupt context wouldn't appear
> on the console (but they would make it to the logfile). Or
> maybe they will, but delayed a bit.
Why? Does printk bypass the normal text console driver?
> Question is: is this worth the effort, or are people
> OK with just running X or vgacon all the time?
Well, I run X most of the time, but I always have fbcon running, and
use it occasionally. I could probably live with latency peaks when
*using* the consoles on fbdev, but I'd be somewhat annoyed with
facing a true text mode when kicking "the eXtended resource hog". Not
the end of the world, though, at least not now.
> (*) Easy to fix for Voodoo 3, TNT2 and G200. That's
> all I have :)
G400? :-) Basically the same code as for the G200? (Usually the same
drivers, with some code that's only used on the G400, AFAIK.)
//David
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