[Beowulf] Threaded code

Joe Landman landman at scalableinformatics.com
Tue Aug 17 08:45:36 PDT 2004

Mark Hahn wrote:

>>variables? (do you have an NCPU=1 or something like that hanging around?)
>afaikt, when threads are enabled, atlas compiles in the number of threads,
>based on what it detects on the machine doing the compilation.  so, for
>instance, if you happened to compile atlas on this machine with the uni
>kernel, (or some other uni) you'd get no threads.  this is a bit
>counterintuitive to anyone used to OMP_NUM_THREADS, but it certainly
>makes sense for atlas.

Ok, I haven't used atlas in a while.  Are you saying that it hardcodes 
the number of processors into the code itself?  Wouldn't this 
effectively render binary RPMs of Atlas completely useless?  Would also 
make building static binaries (don't know if it is possible with Atlas 
libs) a waste of time if you need a portable binary.

>>Are you sure you are using only one CPU (e.g. what tests are you using 
>>that indicate a single CPU)?
>yes, another good question.  if you simply don't get any speedup from using
>threads, it doesn't necessarily imply that you're not using threads ;)

I have had codes that spent very little time in the parallel sections in 
the past.  Simply adding another processor/thread does not automagically 
half the run-time.  You would need to use some of the more advanced 
query tools to see what is going on.


>regards, mark hahn.

Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics LLC,
email: landman at scalableinformatics.com
web  : http://www.scalableinformatics.com
phone: +1 734 612 4615

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