[Beowulf] Optimal BIOS settings for Tyan K8SRE

[Mark Hahn]

> 270s) which are being used primarily for Oceanographic modelling (MPICH2
> running on Debian/Linux 2.6 kernel).

on gigabit?

> I had to make some tweaks to make all 4GB of RAM visible to the OS.

how much was missing, and was it just graphics aperture-related?

> 	HT-LDT Frequency	Auto
> 	Dual-Core Enable	Enabled
> 	ECC Features
> 		ECC	Enabled
> 		ECC Scrub Redirection	Enabled
> 		Dram ECC Scrub CTL	Disabled
> 		Chip-Kill	Disabled
> 		DCACHE ECC Scrub CTL	Disabled
> 		L2 ECC Scrub CTL	Disabled

those seem to be normal settings I see on most machines.  the RAS-related
settings seem to be unnecessary for a "normal" cluster (one where no large
rate of ECC's happen, and one where a reboot doesn't cause planes to fall
out of the sky.)

on the other hand, I'd love to find out whether there is any performance
impact from enabling scrub, since it does slightly increase memory workload.
then again, if your rate of correctable ECCs is trivial, scrubbing is not 
relevant...

> 	Memory Hole
> 		4GB Memory Hole Adjust	Manual
> 		4GB Memory Hole Size	768 MB
> 		IOMMU	Enabled
> 		Size	32 MB
> 		Memhole mapping	Hardware

I don't think there are performance implications here.  you seem to have
already found the right combination of iommu/memhole settings that give
you your full roster of ram.  my googling on the topic didn't enlighten 
me much, though people apparently recommend "iommu=memaper=3"

> 	Memory Config
> 		Swizzle Memory Banks	Enabled

donno - I don't think this appears in the AMD bios-writers guide

> 		DDR clock jitter	Disabled
> 		DDR Data Transfer Rate	Auto
> 		Enable all memory clocks	Populated
> 		Controller config mode	Auto
> 		Timing config mode	Auto

those are the settings I normally see as well.

> 	AMD PowerNow!	Disabled
> 	Node Memory Interleave	Auto
> 	Dram Bank Interleave	Auto

for numa-aware OS's (like any modern linux), I think node-memory 
interleave should be disabled.

regards, mark hahn.