Re: [Linux-fbdev-devel] [PATCH] Disable mach64 accelerator if stride is not multiple of 64

[Mikulas P. <mpa...@re...>]

On Thu, 18 Jun 2009, krz...@po... wrote:

> > Mikulas Patocka napisa³(a):
> > 
> > 
> > BTW. why doesn't it use accelerator for screen scrolling? It seems to 
> > redraw all non-empty characters, which is fast if most of the screen is 
> > empty but gets slower if the screen is full of text.
> > 
> 
> It uses the accelerater.. The screen redraw uses accelerated imageblit() function 
> if it exists.
> In order to use the blitter one must define FBINFO_READS_FAST flag. However,
> it may not end up faster. It is faster if the memory is fast while chip is not
> so fast relatively (e.g. all new GeForce and Radeon chips, 3DFxx Voodoo3+ have 
> very fast memory attached).
> It  may vary for other chips, i.e. even if your ati card equiped with sgram it is 
> faster it may be slower for the same chip with sdram.
> 
> Also, if blitter is used for scrolling the crolling speed goes down with increasing 
> pixel depth which is not a case for the redraw method.
> 
> Regards,
> Krzysztof

I tried to define FBINFO_READS_FAST. At some tests it was as fast as 
without it, at some it was about 20% faster.

So the only way how to avoid this slow-scroll annoyance would be to batch 
the updates --- i.e. don't scroll after each line of output but scroll 
after for example 5 lines. But it would mean major code redesign...

Mikulas