[ydl-gen] YDL6 and G5 w/Radeon 9600 performance tips

[rarob at comcast.net]

Hello all,
  Just wanted to post a few observations about what I've seen with YDL6.  My computer is a dual 2Ghz G5
PowerMac with the Radeon 9600 graphics card (the beastie with the DVI and the ADC connectors).  I'd 
noticed a fairly significant performance hit when moving from YDL4.0.91 to YDL6 (long story for staying
with 4.0.91 for so long...), on the order of 4x or so *especially* when using graphics.  I've got two
Sceptre X20WG LCD's attached, and YDL6 was the first linux I've been able to get true 'stable' dual
head graphics on.  
  Anyway, after going back and forth with some of the kernel developers and some folks from Xorg I've
gotten rid of most of the performance degradations.  The changes were in two chunks:

STEP 1 - X11 configuration
 My initial Xorg config came from running 'Xorg -configure'.  This gave me a working X11 with
the same display on both monitors.  I was able to use '/usr/bin/system-config-display' (or the
menu equivalent) to change to a multi-head display.  Note however that the display tool
wasn't able to save the new setup *IF* the second monitor was configured as a 'generic 1680x1050'.
So I set it to 'generic 1280x1024', and then edited /etc/X11/xorg.conf to fix this.
  I also edited /etc/X11/xorg.conf to set "Clone" to "False", and the drivers to "radeon" instead of "ATI".  The
kicker is to *also* set the "AccelMethod" options to "EXA".  Seems there is a bug where XAA (the default)
causes a severe performance hit.

STEP 2 - kernel configs
  My initial suspicions for the slowdown were aimed at the kernel, since I was seeing problems even when 
graphics were not in use.  I did these changes *first*, then found out about the X11 issues above, so I don't
know how much of an effect these mods had, although I did see some improvement after doing these.  
At any rate, I downloaded the 2.6.25-rc8 kernel and rebuild after tweaking some kernel configs:
64 bit kernel
processor support -> opt for power4, altivec, SMP (maxcpus=2)
platform support -> machine type (generic),  *only* apple powermac for machines


Again, don't know if the kernel rebuild played much of a factor.  I saw some performance gains
after doing the kernel mods, but the real speedup came after tweaking the X11 setup.

Hope this might help someone else...  I liked YDL6 alot (performance issue was a growing concern), but life
is much better now.....


Rob