Re: k8-smp

[Lennart Sorensen <lsorense@csclub.uwaterloo.ca>]

On Tue, Jun 06, 2006 at 10:12:33AM +0200, Francesco Pietra wrote:
> After the installation of amd64 etch with generic kernel, I chose a kernel for 
> multi dual opteron.
> uname -a reports:
> Linux debian 2.6.15-1 amd64-k8-smp # SMP
> 
> In view of compilation, I I wonder about the following:
> 
> Dual (or more) Opteron designs are not SMP (Symmetric Multi Processor), but 
> NUMA (Non-Uniform Memory Architecture). With SMP the two CPUs share the same 
> bus to memory, but with NUMA each CPU hassome local memory connected to a 
> local memory bus. The other CPU can still get to that memory, but it's a bit 
> slower. If you would only putin 1x 2GB, you will severely slow down the other 
> CPU cause it has to go through the other CPU to do memory accesses. See 
> ftp://ftp.tyan.com/datasheets/d_s2895_101.pdf 
> The cpu design may have a bearing for the compilation of programs for 
> multiprocessor systems, like mpqc (in the compilation notes, mpqc refers 
> to "symmetric multiprocessor", see 
> http://www.mpqc.org/mpqc-snapshot-html/compile.html.

They _are_ SMP.  Every processor is identical and of the same speed.
The fact memory access speed is not symetric doesn't mean the CPUs
aren't.

> Do smp specified on kernel and NUMA for the opteron characteristics fit 
> together? I can imagine that SMP specified on the kernel chosen simply refers 
> to the presence of more than one dual-opteron. Anyway, it is a bit confusing 
> because it might be seen in conflict with the NUMA characteristics of 
> opteron.

SMP simply refers to more than one cpu thread/core/whatever executes
code.  Intel's hyper threading, dual core, multiple processors, all
require SMP.

> If it is a silly question, I beg pardon.

Not silly.  It is getting somewhat confusing.

Len Sorensen