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

[Owen Stampflee]

Awesome info Rob! Can we post this to the website?

I will also see about posting an updated kernel in errata that fixes 
this, but I'm not sure its feasible (breaking Cell/Power5 would not be 
good).

Cheers,
Owen

rarob at comcast.net wrote:
> 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
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