HPC has been easy for a while ...
When buying new workstations or personal computers, it is easy to adopt the simple mantra that a newer processor or higher clock frequency means your application will run faster. It is not totally true, but it works well enough. However, with High Performance Computing, HPC, it is more complicated.
HPC works by using parallel computing – the use of many computing elements together. The nature of these computing elements, how they are combined, the hardware and software ecosystems around them, and the challenges for the programmer and user vary significantly – between products and across time. Since HPC works by bringing together many technology elements, the interaction between those elements becomes as important as the elements themselves.
Whilst there has always been a variety of HPC technology solutions, there has been a strong degree of technical similarity of the majority of HPC systems in the last decade or so. This has meant that (i) code portability between platforms has been relatively easy to achieve and (ii) attention to on-node memory bandwidth (including cache optimization) and inter-node scaling aspects would get you a long way towards a single code base that performs well on many platforms.
Increase in HPC technology diversity
However, there is a marked trend of an increase in diversity of technology options over the last few years, with all signs that this is set to continue for the next few years. This includes breaking the near-ubiquity of Intel Xeon processors, the use of many-core processors for the compute elements, increasing complexity (and choice) of the data storage (memory) and movement (interconnect) hierarchies of HPC systems, new choices in software layers, new processor architectures, etc.
This means that unless your code is adjusted to effectively exploit the architecture of your HPC system, your code may not run faster at all on the newer system.
It also means HPC clusters proving themselves where custom supercomputers might have previously been the only option, and custom supercomputers delivering value where commodity clusters might have previously been the default.