[Beowulf] Threaded code

Art Edwards arthur.edwards at kirtland.af.mil
Tue Aug 17 16:23:18 EDT 2004


Thanks for the input. We have determined that our atlas build is,
indeed, threaded, and that it is reasonably well tuned for this system.
For an 800x800 system we see the following for dgemm

/usr/lib64/libblas.a       430.540 MF
ATLAS no threads	   3053.107 MF
ATLAS with pthreads	   5115.086 MF

1.67 is our speed up for 800x800. Now we have to learn about building
a threaded fortran application. Are there any compiler swithes we need
for g77 to build threaded code?

Art Edwards


On Tue, Aug 17, 2004 at 01:52:24PM -0400, Robert G. Brown wrote:
> On Tue, 17 Aug 2004, Art Edwards wrote:
> 
> > I mean that when we run the threaded code and look at top, don't see two
> > processors running. The load is always less than or equal to one. When
> > we run two separate jobs, we see a load of 2. 
> 
> If you see a load of 2 and they complete in the time of 1, nothing is
> wrong with SMP or the two processors, but your code, threaded or not,
> isn't running in parallel.  As Mark suggested earlier, that makes me
> suspect that your copy of ATLAS is either not threaded or not built for
> your (SMP) system or both.
> 
> I'd suggest doing a proper build of ATLAS >>just<< for that system,
> exploring the build options enough to be sure that the options you are
> shooting for are turned on.  I also wouldn't be terribly surprised if
> ATLAS doesn't speed up a whole lot when multithreaded.  It depends a bit
> on where it is bottlenecked -- if it is bottlenecked at a shared
> resource point, it could even slow down.  You're right back to the
> fundamental problem of parallel program design -- it is very difficult
> to automate because there are so many ways things can interact and
> because work cannot always be done faster in parallel.
> 
>    rgb
> 
> > 
> > Art Edwards
> > 
> > On Tue, Aug 17, 2004 at 07:45:32AM -0700, Alvin Oga wrote:
> > > 
> > > hi ya
> > > 
> > > yup.. that is dual cpu
> > > 
> > > On Tue, 17 Aug 2004, Art Edwards wrote:
> > > 
> > > > We are running SuSE 9.1 on a system with 8 GB of ram and two scsi disks.
> > > > Here is /proc/cpuinfo
> > > > processor       : 0
> > > 
> > > good
> > > 
> > > > processor       : 1
> > > 
> > > good
> > > 
> > > > Linux bladerunner 2.6.4-52-smp #1 SMP Wed Apr 7 01:58:54 UTC 2004 x86_64
> > > > x86_64 x86_64 GNU/Linux
> > > 
> > > good
> > > 
> > > 
> > > > > Newbie question:
> > > > > 
> > > > > We just purchased a dual opteron box that is running an SMP kernel. We
> > > > > have built a fortran code using g77 and a pthreaded atlas. Currently, we
> > > > > see only one processor. What really simple thing have we missed?
> > > 
> > > so what do you mean by "see only one processor" ??
> > > 
> > > c ya
> > > alvin
> > 
> > 
> 
> -- 
> Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
> Duke University Dept. of Physics, Box 90305
> Durham, N.C. 27708-0305
> Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu
> 
> 

-- 
Art Edwards
Senior Research Physicist
Air Force Research Laboratory
Electronics Foundations Branch
KAFB, New Mexico

(505) 853-6042 (v)
(505) 846-2290 (f)
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