to interleave or not to interleave...

[David O'Brien]

On Thu, May 05, 2005 at 12:08:21PM -0600, Ken Gunderson wrote:
> Searching for enlightenment and I'm not a memory guru nor kernel hacker
> here so could use some help understanding this. System is a Tyan
> B2882T26 w/ a pair of 246's.

This uses the Tyan s2882 motherboard, which is really what the question
centers around.


> I've two 1GB sticks of Corsair ECC
> Registered memory onhand.  Question is whether it would be "best" to: 
> 
> 1) put both cpu0 dimm slots 1 & 2
> 2) put 1 in dimm slot 1 of each cpu
> If I understand correctly, config 1 results in 128 bit interleaved while
> config 2 results in 64 bit non-interleaved.  (config 1 leaves cpu 0 as
> memory "controller" for cup 1?).

Correct.

Using both of your DIMMs in one CPU means you do 128-bit (dual-channel)
memory accesses, but your 2nd memory controller is idle.  And you are
guarenteed the 2nd CPU will always go across the Hypertransport link for
memory accesses.
Putting one DIMM in each CPU means you only do 64-bit (single-channel)
memory accesses, but you are able to have both memory controllers active.


> I've read some stuff where
> interleaved results in faster access but also can have "miss"
> penalaties.  Any explanations on where one strategy is better than
> other appreciated.

This is a hard question to answer.
The real answer is to get another 2 DIMM's.  

-- 
-- David  (obrien at FreeBSD.org)