OpenMP in Small Bites/NUMA

HPC.NRW
Other HPC Courses
1.	Gprof Tutorial
2.	Introduction to Linux in HPC
OpenMP in Small Bites
1.	Overview
2.	Worksharing
3.	Data Scoping
4.	Non-Uniform Memory Access

Quiz

1. Why is it important to initialize your data in parallel when executing on a NUMA architecture?

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2. Why is it important to bind the threads?

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3. Given a NUMA architecture with to two sockets with six cores each: How can you place the threads of an OpenMP program running with 4 threads among both sockets and bind them to a core?

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   Why is it important to initialize your data in parallel when executing on a NUMA architecture? (Initializing the data in parallel distributes the date amoung the different sockets. When accessing the data in a hotspot region in the same pattern you avoid remote memory accesses.)
   Why is it important to bind the threads? (Otherwise the operating system might decide to migrate the thread from one core to anothers. This results in a performance penalty due to the context switch and a potential remote data access on NUMA architectures.)
   Given a NUMA architecture with to two sockets with six cores each: How can you place the threads of an OpenMP program running with 4 threads among both sockets and bind them to a core? (Set OMP_PROC_BIND=spread and OMP_PLACES=cores )