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List:       xfree-xpert
Subject:    Re: [Xpert]Asus portable with Silicon Motion Lynx 3DM
From:       Mark Vojkovich <mvojkovich () nvidia ! com>
Date:       2002-03-31 23:59:32
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On Sun, 31 Mar 2002, Vladimir Dergachev wrote:
> 
> On Sun, 31 Mar 2002, Egbert Eich wrote:
> 
> > Mark Vojkovich writes:
> >  >
> >  >    Looking at the code for the siliconmotion driver in the tree, I'm
> >  > not surprised.  It looks like the driver is polling until the retrace
> >  > everytime it has to put a frame.  I would expect that to eat up more
> >  > CPU than just doing all the video in software.   You should probably
> >  > try it without Xv, if that's being used now.  Or somebody should fix
> >  > the drivers.
> >  >
> >
> > OK, I will look into this next week.
> >
> > I guess this retrace waiting was done to prevent shearing.
> > Only very few chipsets support some kind of double buffering
> > with automatic buffer switching on retrace. On all others
> > we need to poll the chip to detect a retrace.
> 
> Well, I know that ATI chipsets did this at least since Rage Pro. Also,
> AFAIK, mga does it too and I would be surprised if nvidia does not do it.
> 
> The way it is implemented in ATI chips is that registers that describe a
> buffer in ram are buffered with new values taking effect after retrace.
> I do not think this takes any significant amount of chip real estate.
> So there should not be any reason not to implement this.
> 

   I agree, but I wouldn't be surprised if some low-end chips didn't
support this anyhow.

   Egbert, if you can program the registers outside of the retrace
without hardware gliches, I think you should just do that.  Polling
for the retrace in the server should not be done for stuff like this.
These apps are typically cpu intensive so they are competing with 
the server for CPU.  That means the server might not even be scheduled
during the retrace a good deal of the time.  I suspect the server
spends its entire slice spinning most of the time.


				Mark.


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