[Beowulf] Optimal BIOS settings for Tyan K8SRE

[Bruce Allen]

On Sun, 3 Sep 2006, Mark Hahn wrote:

>> 	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

You can find our systems BIOS/ECC/Scrub settings here:
http://www.lsc-group.phys.uwm.edu/beowulf/nemo/construction/BIOS/bios_settings.txt
Our systems are Supermicro H8SSL-i motherboards, with a 
Serverworks/Broadcom HT1000 chipset and a single Opteron 175 (dual core, 
2.2 GHz).

The ECC part is:
  DRAM ECC Enable = Enabled
  MCA DRAM ECC Logging = Enabled
  DRAM Scrub Redirect = Enabled
  DRAM BG Scrub = 2.62ms
  L2 Cache BG Scrub = 84.00ms
  Data Cache BG Scrub = 84.00ms

Scrubbing is done one cache line (64) bytes at a time.  Thus with 2GB of 
memory and DRAM background scrub interval of 2.62ms we will scrub the 
entire memory in approximately:

2 GB/64 Bytes * 2.62 ms = 2^31 / 2^6 * 2.62 ms = 87912 secs

So our choices correspond to one complete scrub of DRAM per day.  Our 
settings scrub the L2 cache more often: about once every half hour.  Just 
modify the calculation above, using 1MB instead of 2GB, and 84 ms instead 
of 2.62 ms.  One finds that the L2 cache is scrubbed about once every 1376 
seconds (every 23 minutes).

Cheers,
 	Bruce