CODEWITHSUNDEEP
pthreadsmpiopenmpi
xhe8
xhe8

Reputation: 439

MPI/Pthread program does not scale

I have a MPI/Pthread program in which each MPI process will be running on a separate computing node. Within each MPI process, certain number of Pthreads (1-8) are launched. However, no matter how many Pthreads are launched within a MPI process, the overall performance is pretty much the same. I suspect all the Pthreads are running on the same CPU core. How can I assign threads to different CPU cores?

Each computing node has 8 cores.(two Quad core Nehalem processors) Open MPI 1.4 Linux x86_64

Upvotes: 0

Views: 935

Answers (1)

Ryan Marcus
Ryan Marcus

Reputation: 1026

Questions like this are often dependent on the problem at hand. Most likely, you are running into a resource lock issue (where the threads are competing for a lock) -- this would look like only one core was doing any work, because only one thread can (effectively) do any work at any given time.

Setting CPU affinity for a certain thread is not a good solution. You should allow for the OS scheduler to optimally determine the physical core assignment for a given pthread.

Look at your code and try to figure out where you are locking where you shouldn't be, or if you've come up with a correct parallel solution to the problem at hand. You should also test a version of the program using only pthreads (not MPI) and see if scaling is achieved.

Upvotes: 0

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