By Paul Parkinson
There's an interesting editorial column 'Multicore Processing Becomes the New Mainstream' in the latest edition of COTS Journal. Jeff Child discusses how multicore processors, after becoming all pervasive in the desktop and server market, are now becoming the norm for embedded aerospace and defence systems. He also shares some insights into why the transition to multicore is necessary, and provides an example of the deployment of multicore in the Aegis Modernization Program (Congressional Research Service report on FAS website: PDF).
Rather tantalizingly, Jeff only mentions software architectures in his final paragraph (maybe that's a subject for a future editorial), where he contrasts the use of Symmetric Multiprocessing (SMP) on multicore devices with tiled processors (which can be massively parallel architectures).
As a software engineer, I think this is where things start to get really interesting, and there are actually quite a number of different possible permutations on homogeneous multicore architectures when you include visualization using a hypervisor into the overall software architecture. This can support a system with separate instances of an operating system or runtime per core, known as asymmetric multiprocessing (AMP); or a single instance of an operating system running across multiple cores, known as symmetric multiprocessing (SMP), or even a combination of both.
Customers often ask me 'Which is better, AMP or SMP?', and my answer is 'It depends'. It depends on the nature of their application, the degree of parallelism within it which determines the scalability across cores; it depends on the I/O architecture and throughput requirements and more besides. But by analyzing the system requirements in detail, these can be mapped to a suitable implementation which may comprise AMP, SMP or both. Bill Graham discusses how this complexity can be simplified into a number of key uses cases in this recent blog.
Back to the COTS Journal editorial, Jeff also mentions that tiled processors (and massively parallel architectures in general) present a programming challenge due to the complexity involved. This subject was also recently discussed in some technical depth by Mark Hermeling in a recent blog 'A sea of cores, now what?'.