[PATCH] framebuffer: bit_putcs() optimization for 8x* fonts

[PATCH] framebuffer: bit_putcs() optimization for 8x* fonts

This trivial patch gives a performance boost to the framebuffer console

Constructing the bitmaps that are given to the bitblit functions of the
framebuffer drivers is time consuming.  Here we avoide a call to the slow
fb_pad_aligned_buffer().  The patch replaces that call with a simple but
much more efficient bytewise copy.

The kernel spends a significant time at this place if you use 8x* fonts.
Every pixel displayed on your screen is prepared here.

Some benchmark results:

Displaying a file of 2000 lines with 160 characters each takes 889 ms
system time using cyblafb on my system (I´m using a 1280x1024 video mode,
resulting in a 160x64 character console)

Displaying the same file with the enclosed patch applied to 2.6.13 only
takes 760 ms system time, saving 129 ms or 14.5%.

Font widths other than 8 are not affected.

The advantage and correctness of this patch should be obvious.

Signed-off-by: Knut Petersen <Knut_Petersen@t-online.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>