I did some simple benchmarking (time cat linux-2.6.7-mm5/MAINTAINERS)
between 2.4 and 2.6 and I am not satisfied with what I see (It's claimed
that fbdev-2.6 is faster than 2.4).  The reason for the claim:

2.4 putcs - draw small amounts of data a lot of times
2.6 putcs - draw larger amounts of data a fewer times

The way characters are drawn in 2.6 is optimal for accelerated drivers but
should also give a speed boost for drivers that rely on software drawing.
However the penaly incurred when preparing a large bitmap from a number of
small bitmaps is currently very high.  This is because of the following
reasons:

1 fb_move_buf_{aligned|unaligned} uses pixmap->{out|in}buf.  This is very
  expensive since outbuf and inbuf methods process only a byte or 2 of data
  at a time.

2 fb_sys_outbuf (the default method for pixmap->outbuf) uses memcpy().
  Not a good choice if moving only a few bytes.

3 fb_move_buf_unaligned (used for fonts such as 12x22) also involves a
  lot of bit operations + a lot of calls to outbuf/inbuf which
  proportionately increases the penaly.

So, I thought of separating fb_move_buf_* to fb_iomove_buf_* and
fb_sysmove_buf_*. 

	fb_iomove_buf_* - used if drivers specified outbuf and inbuf methods
	fb_sysmove_buf_* - used if drivers have no outbuf or inbuf methods

	*Most, if not all drivers fall in the second category.

Below is a table that show differences between 2.4, 2.6 and 2.6 +
abovementioned changes.  To reduce the effect of panning and
fillrect/copyarea, the scrollmode is forced to redraw.

=================================================================
Test Hardware: P4 2G nVidia GeForce2 MX 64
Scrollmode: redraw

time cat linux-2.6.7-mm5/MAINTAINERS

1024x768-8		1024x768-16		1024x768-32
=================================================================
8x16 noaccel (2.4)
real    0m5.490s	real    0m8.535s	real    0m15.388s
user    0m0.001s	user    0m0.000s	user    0m0.001s
sys     0m5.487s	sys     0m8.535s	sys     0m15.386s

8x16 noaccel (2.6)
real    0m5.166s	real    0m7.195s	real    0m12.177s
user    0m0.001s	user    0m0.000s	user    0m0.000s
sys     0m5.164s	sys     0m7.192s	sys     0m12.176s

8x16 noaccel+patch (2.6)
real    0m3.474s	real    0m5.496s	real    0m10.460s
user    0m0.001s	user    0m0.001s	user    0m0.001s
sys     0m5.492s	sys     0m5.492s	sys     0m10.454s
=================================================================
8x16 accel (2.4)
real    0m4.368s	real    0m9.420s	real    0m22.415s
user    0m0.001s	user    0m0.001s	user    0m0.001s
sys     0m4.019s	sys     0m9.384s	sys     0m22.312s

8x16 accel (2.6)
real    0m4.296s	real    0m4.339s	real    0m4.391s
user    0m0.001s	user    0m0.001s	user    0m0.000s
sys     0m4.280s	sys     0m4.336s	sys     0m4.389s

8x16 accel+patch (2.6)
real    0m2.536s	real    0m2.649s	real    0m2.799s
user    0m0.000s	user    0m0.000s	user    0m0.001s
sys     0m2.536s	sys     0m2.645s	sys     0m2.798s
=================================================================

1024x768-8		1024x768-16		1024x768-32
=================================================================
12x22 noaccel (2.4)
real    0m7.883s	real    0m12.175s	real    0m21.134s
user    0m0.000s	user    0m0.000s	user    0m0.001s
sys     0m7.882s	sys     0m12.174s	sys     0m21.129s

12x22 noaccel (2.6)
real    0m10.651s	real    0m13.550s	real    0m21.009s
user    0m0.001s	user    0m0.001s	user    0m0.000s	
sys     0m10.617s	sys     0m13.545s	sys     0m21.008s

12x22 noaccel+patch (2.6)
real    0m4.794s	real    0m7.718s	real    0m15.173s
user    0m0.002s	user    0m0.001s	user    0m0.000s
sys     0m4.792s	sys     0m7.715s	sys     0m15.170s
=================================================================
12x22 accel (2.4)
real    0m3.971s	real    0m9.030s	real    0m21.711s
user    0m0.000s	user    0m0.000s	user    0m0.000s
sys     0m3.950s	sys     0m8.983s	sys     0m21.602s

12x22 accel (2.6)
real    0m9.392s	real    0m9.486s	real    0m9.508s
user    0m0.000s	user    0m0.000s	user    0m0.001s
sys     0m9.392s	sys     0m9.484s	sys     0m9.484s

12x22 accel+patch (2.6)
real    0m3.570s	real    0m3.603s	real    0m3.848s
user    0m0.001s	user    0m0.000s	user    0m0.000s
sys     0m3.567s	sys     0m3.600s	sys     0m3.844s
=================================================================


Summary:

1 2.6 unaccelerated is a bit faster than 2.4 when handling 8x16 fonts,
  with a higher speed differential at high color depths.

2 2.4 unaccelerated is a bit faster than 2.6 when handling 12x22 fonts,
  with a smaller speed difference at high color depths (2.6 is actually a
  bit faster than 2.4 at 32bpp).

3 2.4 rivafb accelerated suffers at high color depths, even becoming
  slower than unaccelerated, possibly because of the 'draw few bytes many
  times' method.

4 2.6 rivafb accelerated has similar performance at any color depth,
  possibly because of 'draw lots of bytes a fewer times' method.

5 With the changes, there is a speed gain of ~1.7 seconds and ~5.7
  seconds with 8x16 and 12x22 fonts respectively indepependent of the color
  depth or acceleration used.  The speed gain is constant but significant.

Below is a patch against 2.6.7-mm5.  The effects will be very noticeable
with drivers that uses SCROLL_REDRAW, but one should still see some speed
gain even if SCROLL_YPAN/YWRAP is used.


Separated fb_sys_move_* into fb_iosys_move_* and fb_sysmove_* to reduce
penalty when constructing fb_image->data from character maps.  In my
testcase (1024x768 SCROLL_REDRAW), I get a ~1.7 second advantage with 'time
cat MAINTAINERS' using 8x16 fonts and ~5.7 seconds with 12x22 fonts.  The
speed gain is independent of acceleration or color depth.
Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>