Re: dual core processors

From: Jimmy Tang (jtang_at_tchpc.tcd.ie)
Date: Fri Mar 31 2006 - 12:38:24 CST

Hi Leandro,

On Fri, Mar 31, 2006 at 05:04:01PM +0000, Leandro Martínez wrote:
> Dear namd users,
> We have recently installed a cluster with AMD Athlon 64 X2 Dual-Core
> processors. My question is about how this dual core processor must behave:
>
> 1. As if they were really two processors? They should be seen as two
> processors
> in the cpu? Should I use a SMP kernel? Should I launch two namd processes
> for
> each dual-core processor? If I launch two processes they should be seen in
> top
> using both 100% cpu as in a typical two-processor cpu?

AMD64 x2 cpus, have two physical cores on one die/packaging, so if you
run a SMP kernel it will use both cores for processing, so yes you should
treat them as two physical cpu's. the only catch is the memory bandwidth
to the packaged cores isnt the same as a real dual cpu machine. the memory
bandwidth to the amd64 x2 is halved if you throw alot of data at the
cpu. (since the number of pins on the packaged cpu is still 939 even
thogh there are two physical cores) you'll probably find both cores will
run ~80% peak usually which is pretty good considering the price of the
chips compared to opterons.

>
> 2. It must be considered a single processor, appear as a single processor
> and
> the dual-core mechanism will distribute tasks by itself. I should launch
> only
> one namd process per cpu and a single-processor kernel must be used?

not too sure on how to answer this, but you could probably run two mpi
processes or two namd tcp processes on a single amd64 x2 cpu without
much problems. or if your programs are multithreaded, just run it with
two threads.

Jimmy

-- 
Jimmy Tang
Trinity Centre for High Performance Computing,
Lloyd Building, Trinity College Dublin.
http://www.tchpc.tcd.ie/

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