Hello world :-) This post on LinkedIn by Laurie Laurie Kirk inspired me, as I know Raiden is working on x86/AMD64 port of NuttX, and I have recenlty upgraded my main desktop to Intel Ultra9 285K that has 36 MB Intel Smart Cache / 40MB L2 Cache. Maybe a nice challenge to see it NuttX can run entirely from CPU Cache too as we run it on MCUs below 16KB Flash and 8KB RAM? :-)
What if an OS fit entirely inside the CPU’s Cache? Turns out we’ve been doing it for decades. CNK, the OS for IBM’s Blue Gene Supercomputer, is just 5,000 lines of tight C++. Designed to “eliminate OS noise”, it lives in the cache after just a few milliseconds of boot. — Kernels that “live” in the cache are common for HPC. Cray’s Catamount microkernel (~2005) used a similar method for jitter free timing. Huge Pages, Statically Mapped Memory, and a lack of scheduling are all typical aspects of these systems. What about the modern era? — Modern CPUs are *insane*. L3 sizes exceed GIGABYTES per socket (see Genoa). Many HPC labs run the hot path in light kernels (LWKs), outsourcing file I/O and syscalls to separate nodes; all with the intent of reducing µs-level jitter. Determinism is the name of the game. — Fujitsu uses 48 LWK cores for every 2 “assistant” Linux cores in their Fugaku supercomputer. Sandia prefers Linux (RHEL), but special queues request their homegrown LWK “Kitten”. In the OSS world, projects like HermitCore and Unikraft see experimentation in the Cloud space. -- CeDeROM, SQ7MHZ, http://www.tomek.cedro.info
