Re: Blitter speed tests (was: smart blitterusage for scr olling)

["Antonino A. Daplas" <adaplas@gmail.com>]

On Fri, 2007-05-11 at 08:00 +0200, Krzysztof Helt wrote:
> Dnia 10-05-2007 o godz. 22:36 Antonino A. Daplas napisał(a):
> > On Fri, 2007-05-11 at 04:24 +0800, Antonino A. Daplas wrote:
> > > If you do, it might even be wise to change the default from
> > > SCROLL_REDRAW to SCROLL_MOVE...?
> > > 
> > Come to think of it we'll probably just let the driver choose
> the scroll
> > method.
> > 
> > SCROLL_MOVE is faster at lower bit depths because the bitmap
> preparation
> > for the putcs method slows down SCROLL_REDRAW.  But as the bit
> depth
> > goes up, the amount of data moved by bmove goes up but at a
> higher rate
> > than the data moved by putcs. Thus SCROLL_MOVE loses its edge
> at 16-32
> > bpp. At what point these lines intersect we really don't know as it
> > depends on the hardware and the driver's imageblit/copyarea
> > implementation.
> > 
> 
> If you want really complicated solution one can switch
> FB_READS_FAST flag depending on the bit depth inside each driver ;-)

I was actually thinking of that, but I'm not considering it anymore.
It's too complicated and there are too many unknowns.

> 
> I think that a simple solution is to leave everything untouched
> except tdfxfb and nvidiafb drivers. These two should add
> FB_READS_FAST flag permanently to use  blitter for scrolling.
> 

Yes, I benchmarked this with a Geforce4 MX 4000. Your scroll method
beats scroll_redraw in all cases (all supported resolutions and bit
depths) and the only time the old SCROLL_MOVE was faster is at 640x480
at 8bpp by only a few percent.  At other resolutions and depths, your
scrolling method wins hands down (by a lot).

This is a good patch. Thanks.

Tony


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