[Beowulf] Re: Opteron 275 performance

[Steve Cousins]

On Wed, 27 Jul 2005, 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

Hi Joe,

Thanks a lot.  I just took a look and it seems to make a good case for
getting the Dual Dual Core machine.  

I'm fairly certain that the memory latency issue that Vincent was warning
about won't be an issue, although I'm a bit clueless about how to know for
sure.  How would I go about finding out if our model is TLB trashing main
memory?  I feel like I just bit the hook... I don't want to start a huge
discussion on this but if there are some quick tell-tale signs of it I'd
be interested to find out.

Thanks,

Steve



> 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
> >> 
> >> 
> >> 
> >> 
> >> _______________________________________________
> >> Beowulf mailing list, Beowulf at beowulf.org
> >> To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
> >
> -- 
> Joseph Landman, Ph.D
> Founder and CEO
> Scalable Informatics LLC,
> email: landman at scalableinformatics.com
> web  : http://www.scalableinformatics.com
> phone: +1 734 786 8423
> fax  : +1 734 786 8452
> cell : +1 734 612 4615
> 
>