[Beowulf] Re: Opteron 275 performance

[Philippe Blaise]

Hopefully, you show that dual core is quite superior to 
"hyper"-threading for some scientific programs,
and is cost-friendly, very nice ! but page 14 you write

"It is worth noting that since AMBER8 does consume significant memory 
bandwidth, the
memory contention issue that could reduce overall performance on a AMD 
Opteron 275
processor based 2p/4c system under heavy memory usage shows a small 
effect, at most".

Please, what do you mean by "significant memory bandwith" ? may be no 
more than 50 % ?
have you got an estimation value ?

Philippe.

Joe Landman wrote:

> Hi Steve:
>
>   Not knowing the details of your calculations might be an issue, but 
> you can read about our experiences with a number of chemistry and 
> informatics codes on dual core Opteron systems.  See 
> http://enterprise2.amd.com/downloadables/Dual_Core_Performance.pdf for 
> more details.
>
> Joe
>
> Steve Cousins wrote:
>
>> On Thu, 14 Jul 2005 11:25:12 +0100 Igor Kozin wrote:
>>
>>
>>> But now for 4cores/2CPUs per Opteron node to force the using of
>>>
>>>> only 2 cores (from 4), by 1 for each chip, we'll need to have
>>>> cpu affinity support in Linux.
>>>
>>>
>>> Mikhail,
>>> you can use "taskset" for that purpose. For example, (perhaps not in 
>>> the most elegant form)
>>>        mpiexec  -n 1 taskset -c 0 $code : -n 1 taskset -c 2 $code
>>> But I doubt you want to let the idle cores to do something else in 
>>> the mean time. However small you will generally see an increase in 
>>> performance if you use all the cores.
>>
>>
>>
>> We are considering getting a Dual Dual-Core Opteron system vs. two Dual
>> Opteron systems.  We like the ability to use all four cores on one model
>> but a lot of what we'll do is have two models running at the same time,
>> each using two cores. 
>> We are worried that running two models on one system with four cores 
>> (each
>> model using two cores) will not work as well as using two systems, each
>> with two cores/cpu's.  Is this what you were refering to (Igor) when you
>> wrote:
>>
>>
>>> But I doubt you want to let the idle cores to do something else
>>> in the mean time. 
>>
>>
>>
>> We have an 8 CPU SGI Origin 3200 that has no problem doing this sort of
>> thing.  I'm just curious what the implications are of doing this with 
>> the
>> Dual Core Opteron cpu's. 
>> Thanks,
>>
>> Steve 
>> ______________________________________________________________________
>>  Steve Cousins, Ocean Modeling Group    Email: cousins at umit.maine.edu
>>  Marine Sciences, 208 Libby Hall        http://rocky.umeoce.maine.edu
>>  Univ. of Maine, Orono, ME 04469        Phone: (207) 581-4302
>>
>>
>>
>>
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>
>