On 2/11/20 2:27 PM, Toni Vidal wrote:
That did not solve the problem with step 6. I got the same times.
Indeed I have installed deal.II without threads (DEAL_II_WITH_THREADS =
OFF) and I set in my .basrc OMP_NUM_THREADS=1.
There are many other possible reasons for contention. For example, most
finite element programs are limited by the transfer of data from memory
to the processor. If you have just one program running, then only one
program is using the memory bus and is getting its full speed. But if
you have multiple programs running, then they are all competing for the
same bandwidth on the memory bus, and they will also be slowed down by
more than a single program would be.
It could also be that you have, say, 4 cores on your processor but 3
other programs currently running. Then running one instance of your code
will get a full core, but if you ran four, the total of 7 codes would
have to compete for 4 cores, and all would be slowed down.
By the way, to see whether your program really is using only one thread,
you can run the program 'top' in a separate command line window. It will
show you which percentage of a processor each running job takes up.
Best
W.
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Wolfgang Bangerth email: bange...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/
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