Thank you Alan, this is a nice read, and it touches Cache as RAM (CAR), while I was thinking about putting whole RTOS inside cache :D L1 cache is the fastest memory possible, faster than L2, and a lot faster than DRAM/SRAM, that is faster than any storage drive :-) Just a curiosity :-) Tomek
On Wed, May 21, 2025 at 10:34 PM Alan C. Assis <acas...@gmail.com> wrote: > > Hi Tomek, > > Yes, it is possible, coreboot (LinuxBIOS) did it more than 20 years ago: > https://web.archive.org/web/20200530213938/https://www.coreboot.org/images/6/6c/LBCar.pdf > > But since the computer normally will have DDR memory in the board, there is > not much motivation to do it for NuttX. > > BR, > > Alan > > On Wed, May 21, 2025 at 4:49 PM Tomek CEDRO <to...@cedro.info> wrote: > > > 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 > > -- CeDeROM, SQ7MHZ, http://www.tomek.cedro.info
