Re: RFC: Optimizing putcs()

On 6 Aug 2002, Antonino Daplas wrote:

With fbcon-accel and the new drawing functions in linux-2.5, console
performance degraded compared to the linux-2.4 implementation.  This is
because putcs() has to to do 1 fb_imageblit() per character to be
drawn.  

Yes, this will be shown badly after I'll have ported amifb to the new
framework, since chip RAM accesses are very slow and we use bitplanes...

This can be optimized by letting putcs() initially construct the row of
text to be drawn into an offscreen buffer, then do a single
fb_imageblit() in the end.  Performance wil increase for several
reasons:

Yes, this is very nice! I was thinking about passing an array of images to an
fb_imageblit_multiple() or so, but yours may be better.

For drivers that uses cfb_imageblit or similar, a code such as the one
below can be inserted during initialization:

info->pixmap.addr = (unsigned long) kmalloc(BUFFER_SIZE, GFP_KERNEL);
info->pixmap.size = BUFFER_SIZE;
info->pixmap.offset = 0;
info->pixmap.buf_align = 1;
info->pixmap.scan_align = 1;

Some benchmarks:

time cat /usr/src/linux/MAINTAINERS (40K text file)
mode: 1024x768@8bpp, y-panning disabled.

  [...]

Just for reference, did you run this benchmark on 2.4.x as well?

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds



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