Re: [9fans] nvidia scrolling performance

[erik quanstrom <quanstro@quanstro.net>]

i don't think the extra multiplication has much to do with it.
the system load had esentially zero effect on the drawing time until
both processors were >100% utilization.  at that point, i think that
scheduling, rather than actual cpu usage. (there were occasional long
pauses.)  for moderate loads, the time was +/- 5%.

why does the framebuffer need to be consulted when the background is a known,
solid color?

as far as greyscale fonts go, both cyberbit and code2000 look pretty
good to me.  pelm does not look very good with my monitors large
dot pitch, and allows much less text in the same size window.
i used to use it when i had a better monitor.  also, pelm is fixed-width
and has too many pjws at codepoints that are important to me.

what to you might be slow and ugly might be slow and good looking
to me.  however i'm the one looking at the monitor!

- erik

On Sun Apr 30 10:09:57 CDT 2006, rsc@swtch.com wrote:
> > the only obvious difference i see between the plan 9 driver and the xf86 stuff is
> > that the xf86 stuff tries to buffer dma access a bit.  is ths the key, or should i be looking
> > at something else?
>
> This isn't the nvidia driver.
> The problem is that you're using greyscale fonts.
> That requires dropping into the generic alpha code
> instead of using the boolean alpha code that regular
> character drawing uses.  The boolean alpha code
> avoids some multiplies, which helps a little, and also
> avoids reading from the frame buffer memory, which
> helps a *lot*.
>
> 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.
>
> Now that memories have gotten bigger, it might be
> worth keeping a copy of the screen image like in
> the X port, but it's not clear to me how to reconcile
> that with using acceleration.
>
> Greyscale fonts are slow and ugly.  For more than
> occasional use, just don't do it.
>
> Russ
>
>