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

[Sanders, Rob M.]

Owen,
  Sure, go ahead.  Might want to limit the post at first to the info for the Xorg 
config, and I'm not sure how much of that applies to folks running different
graphics cards.  I'd expect the kernel stuff to not be too much of a problem, but
there are always risks of an rc class kernel being used as production.  
  I want to go back when I have some more time (hopefully the next couple of days)
and start with the stock YDL6 kernel (2.6.23-9ydl6.1) and slowly merge in the config
changes and document the results.  I've got a couple of scripts where I'm changing the
fields in /proc/sys/kernel/sched_features (kernel is compiled with a bunch of debug
enabled) and what what happens.....

Rob



-----Original Message-----
From: yellowdog-general-bounces at lists.terrasoftsolutions.com on behalf of Owen Stampflee
Sent: Thu 4/10/2008 4:25 PM
To: Discussion List for General Yellow Dog Linux User Topics
Subject: Re: [ydl-gen] YDL6  and G5 w/Radeon 9600 performance tips
 
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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