Re: [9fans] nvidia scrolling performance

[erik quanstrom <quanstro@quanstro.net>]

i only have a pci card, but someone with an agp card and a machine that
allows bios-controlled agp bandwidth could eliminate some possibilities.
if it's bus limited, then the total performance should be linear in agp
bus speed, right?  of course we still wouldn't know which direction on
the bus was limiting.

perhaps it's time to add another machine to the second-hand hardware collection.
;-)

pci-x (1.066G/s) has the same bandwidth as PCIe x4 (1G/s).
PCIe SLI = 2 * 16x = 8G/s, which ought to be enough for just about anyone.

- erik

On Sun Apr 30 13:13:21 CDT 2006, steve@quintile.net wrote:
> > Frame buffer memory is very very slow to read from,
> > and not just on nvidia.  When I did some timings six years
> > ago, I found that reading from frame buffer memory
> > was slower than reading from disk.  I'm sure the situation
> > hasn't gotten better.  It's not on the fast path for any
> > other system, so the vendors just don't care.
>
> I may be talking rubbish but I understood this is a fundamental
> problem with reading VGA memory over the PCI bus. VGA cards are
> designed for fast writes and not fast reads.
>
> People have been very interested in using the GCPUs in graphics cards
> to do video processing (to disk rather than for display) but the limiting
> factor seems to have been the speed at which data can be read back.
> I do hear that some cards are appearing with dual PCIX which will allow
> symetric access speeds to the frame buffer.
>
> -Steve
>