[Beowulf] Tyan mobo and /proc/mtrr

[David Mathog]

How do mtrr settings affect performance?  

Anybody know what /proc/mtrr "should" say on various Tyan
mobos?

Three types of Tyan systems here, this is what /proc/mtrr has for each:

S2468UGN    2.6.8.1  (in MDK10.0)
reg00: base=0x00000000 (   0MB), size= 512MB: write-back, count=1
reg01: base=0xf5000000 (3920MB), size=   1MB: write-combining, count=1
S2466N      2.6.8.1  (in MDK10.0)
reg00: base=0x00000000 (   0MB), size=1024MB: write-back, count=1
reg01: base=0xf5000000 (3920MB), size=   1MB: write-combining, count=1
S2466N      2.4.18-10 (in RH7.3)
reg00: base=0x00000000 (   0MB), size=1024MB: write-back, count=1

The first line describes the total memory in the system.
The second line, if present, corresponds to a  setting from
the ATI RAGE XL graphics card.  The ones running the older OS
don't even do that.

Should there be additional mtrr settings, and if so, why?

Note, lspci reports this for the RAGE XL graphics (on all):

        Memory at f5000000 (32-bit, non-prefetchable) [size=16M]
        I/O ports at 1000 [size=256]
        Memory at f4000000 (32-bit, non-prefetchable) [size=4K]

Unclear to me why only 1M of the reported 16M is mapped (apparently)
by the mtrr.  Possibly  this relates to these messages:

  /var/log/messages:Oct 20 12:44:59 safserver kernel: mtrr:\
  0xf5000000,0x400000 overlaps existing 0xf5000000,0x100000

On the other hand, the graphics aren't really used
on the S2466N compute nodes.  Graphics are used more on the
S2468UGN server. Beats me where one would change this value
though.


Thanks,

David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech