Comment 26 for bug 26637

I'm posting what I found here for the record:

1. Disregard all I said from comment #19 down, it makes me look really dumb :-P
It turns out that the APIC options have nothing to do with this, actually I'm
runnig 2.6.15-9-686 now with 'lapic' and all is OK. I only got the idea that
lapic made the 2.6.12 performance drop because at the same time I changed other
things on the grub vmlinuz line...

2. Which brings me to the _real_ culprit. What I had been also messing with was
the vga= option. By default usplash loads vga16fb which on both .12 and .15
_does_ make the performance drop. But vesafb which I used before (in breezy)
works great on .12. But in .15 vesafb also makes the performance drop.

3. After changing the usplash hook and script to load sisfb by default instead
of vga16fb and removing vga= from the boot options all works fine with either
kernel and sisfb even autodetects my LCD size :-)

Conclusion: the sis X driver's memcpy performance depends on the kernel
framebuffer driver that is loaded.