On Sun, 2 Dec 2001, Billy Biggs wrote:
> > > If the mga is so smart, I'm surprised that the XVideo driver buggers
> > > it up. :( Is this a bug do you think?
> >
> > It's a feature. Double buffering takes twice as much video memory and
> > there's not much of it due to the DRI stealing it all for 3D.
>
> But if we can't double-buffer in the hardware then I get tearing, and
> this makes it useless to a DVD player. And you're right, my little
> retrace hack doesn't help much.
>
> What do you recommend?
You should use different hardware or rewrite the mga code to
doublebuffer.
> Why does it take so long to copy the data to the framebuffer? Can't
> we use DMA here? Does it really take that long to just copy 512k?
It's a little more than that because the driver is using
4:2:2 internally. Copying the way it is doing you can't get
much more than 160 MB/sec and uses the CPU the whole time.
DMA won't make the transfer go any faster (it will probably
be slower unless you're using 2x+ AGP), but it won't eat the
CPU. The only drivers that do this are NVIDIA's binary
drivers and supposedly some experimental ATI drivers that
some people are working on. Maybe the i810 drivers do too,
not that it would help, since the bandwidth is probably the
same writing to video ram or the framebuffer.
MArk.
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