[Beowulf] Re: Opteron 275 performance

[Joe Landman]

Hi Philippe:

   I don't have an accurate measurement at this moment.  I have been 
working on measurement using the performance counters.

   What I did not run, but would like to see is a set of streams numbers 
per core, for 1,2,3,4 on the system.

Joe

Philippe Blaise wrote:
> 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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>>
>>
>>

-- 
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics LLC,
email: landman at scalableinformatics.com
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phone: +1 734 786 8423
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