Re: [Linux-fbdev-devel] 2.5.66 fbdev performance (was Re: Re: FBdev updates)

On Fri, 2003-03-28 at 22:19, Petr Vandrovec wrote:

Problem is in the new pixmap handling, especially
pixbuf.output - so now instead of memcpy we
call some function for copying each byte from
font to temporary buffer. As you can see,
"constant" portion of time, independent of
color depth, increased by 1sec for unaccelerated
and by 0.75sec for accelerated putcs.
It is 5% to 25% slowdown (5% for 32bpp unaccelerated,
25% for 8bpp accelerated).

Actually, the slowdown is caused not just by the overhead of the
read/write methods, but also due to the extra work padding and aligning
the bitmaps according to requirements of the hardware.  This was because
James wanted support for buffers located not just in system memory but
also graphics/dma memory.

The result is that unaccelerated imageblit will slow down while properly
written accelerated imageblit will experience some speed up (not much,
probably around 5%).

We can:

1. partially reverse the code so it behaves similarly to 2.5.63. 
Support for writing to graphics/dma memory will go away.  

2. split the code path:  one will go to the '2.5.63' path, the other
will go to the '2.5.66' path, depending on the setting of info->pixmap.

3. keep the code as is

Personally, I prefer #1, but it's up to James/Geert.

Tony