[Beowulf] Optimal BIOS settings for Tyan K8SRE

[Bruce Allen]

I did not check, but would not expect any significant performance impact. 
With the 84 msec choice of scrub times, we are only touching about a dozen 
cache lines (64 bytes each) per second.  I don't see how this could have a 
significant impact on performance.

Cheers,
 	Bruce

On Mon, 4 Sep 2006, stephen mulcahy wrote:

> Hi Bruce,
>
> Do you have any idea what the performance impact from enabling scrubbing
> is on your systems? did you do any before/after benchmarking?
>
> Thanks,
>
> -stephen
>
> Bruce Allen wrote:
>> 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
>
>