This course covers performance engineering approaches on the compute node
level. Even application developers who are fluent in OpenMP and MPI often lack
a good grasp of how much performance could at best be achieved by their code.
This is because parallelism takes us only half the way to good performance.
Even worse, slow serial code tends to scale very well, hiding the fact that
resources are wasted. This course conveys the required knowledge to develop a
thorough understanding of the interactions between software and hardware. This
process must start at the core, socket, and node level, where the code gets
executed that does the actual computational work.
We introduce the basic architectural features and bottlenecks of modern
processors and compute nodes. Pipelining, SIMD, superscalarity, caches,
memory interfaces, ccNUMA, etc., are covered. A cornerstone of
node-level performance analysis is the Roofline model, which is introduced in
due detail and applied to various examples from computational science.
We also show how simple software tools can be used to acquire knowledge
about the system, run code in a reproducible way, and validate hypotheses
about resource consumption. Finally, once the architectural requirements of a
code are understood and correlated with performance measurements, the
potential benefit of code changes can often be predicted, replacing
hope-for-the-best optimizations by a scientific process.