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List:       linux-smp
Subject:    Re: Dual Core vs. Dual CPU
From:       "Robert M. Hyatt" <hyatt () cis ! uab ! edu>
Date:       2006-04-26 20:47:16
Message-ID: Pine.LNX.4.63.0604261544380.14067 () crafty ! cis ! uab ! edu
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Depends on the architecture.  In an AMD opteron-based dual, each cpu has 
a local memory controller and local memory, connected through the 
hypertransport to the other processor through its hypertransport 
interface.  Both processors can access their own local memory with no 
interference whatsoever.  On a dual core, there is a single memory 
controller, shared by two processors, leading to a potential bottleneck. 
There is also a single hypertransport to get to other processors on 
other chips, and that can also be a bottleneck.

But all in all, dual-cores are dynomite for performance, but one needs 
to be careful to avoid the memory bottleneck...



Robert M. Hyatt, Ph.D.          Computer and Information Sciences
hyatt@uab.edu                   University of Alabama at Birmingham
(205) 934-2213                  136A Campbell Hall
(205) 934-5473 FAX              Birmingham, AL 35294-1170

On Wed, 26 Apr 2006, Urs Thuermann wrote:

> Bill Davidsen <davidsen@tmr.com> writes:
>
>> The bad part is that the cores share a bus connection, the good part
>> is that it appears that some IPC can be done on chip.
>
> Why is that bad?  Is that different from a dual CPU system?  I thought
> in a dual CPU system, too, both CPUs share the bus and only one CPU
> can use the bus at a time (as long we're not talking about NUMA, of
> course).
>
> urs
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