Unfortunately, L4 and microkernels in general have (unfairly) gained a bad reputation in some circles, stemming from some projects in the 90s that ended in spectacular failure. Examples include IBM's Workplace OS, which costed billions of dollars in development. L4 has had quiet success in the embedded space. General interest has renewed thanks to interesting projects like the seL4 project.
> I wonder why neither Minix 3 nor Fuchsia are using L4
There are many variants of L4, which have similar concepts and APIs but favour different design choices. So it's not that straight forward. In my opinion, I suspect companies with enough manpower will find it easier to make a new project and take the best ideas of L4 without importing all the controversial or philosophical aspects.
Edit: fixed a typo
Minix 3, a new system with the same name, doesn't predate L4. Tannenbaum probably learned stuff from the L4 people given he cites their work in his microkernel debate with Torvalds. They made a custom kernel since their requirements were different than L4 people's. They might have also thought it would be fun. Lots of researchers like just doing their own thing for the experience.
"L4 has had quiet success in the embedded space. "
Don't understate it: OKL4 claimed deployment in a billion phones mostly for baseband isolation. Got acquired by General Dynamics for big bucks. So, there's one, success story.
EDIT: Still reading the articles. Gernot reminds me PikeOS from Sysgo was "a L4 clone." They got acquired by Thales after quite a few iterations on their PikeOS product. An annual report I found by Thales said they were acquired for over 20 million Euros. Still on low-end in terms of market value but might have been successful depending on money in vs gained.
EDIT 2: Read his blog posts. Before OK Labs Post No 6, here's what he claims about L4 uptake:
"Secondly, a lot of stuff is running on L4: – Qualcomm modem chips have been running our L4-embedded kernel since 2006, that’s a few billion devices – The security processor of all iOS devices is running a modified version of our L4-embedded, that’s another 200-300 million devices every year – seL4 is being deployed on autonomous military air and ground vehicles, with the first autonomous helicopter flight in July 2015 – many other safety- and security-critical deployments are in progress.
I’m not aware of any real-world deployments of Minix."
Of course, we found out later Minix 3 was in Intel's baseband. So, there's two of them with people claiming massive deployments in supporting CPU's/MCU's. What you alluded to didn't refute a large number of units. Just that the company was anything as good as marketing presented. It wasn't. A few deliverables kept selling, though, per same source. He was wrong about Minix 3, too. Probably because it was Intel's secret for a while. I bet they wanted the reliability, included apps/code, and BSD license.
>The Mach kernel (used by macOS and others)
Where/how does this typically manifest itself? Why isn't macOS slow/sluggish?
The macOS kernel had a reputation for sluggishness back in its early days, due (to the best of my understanding) due to the sluggishness of Mach messaging, which is how Mach implements system calls to the kernel. macOS also supports BSD syscalls, and Apple has apparently done enough optimization here that it's now roughly on par with Linux.
Around 2006, Apple did have an internal, experimental version of macOS ("Darbat") which ran Mach on top of the L4 microkernel, but this project was canceled, for whatever reason.
https://www.blackhat.com/docs/us-16/materials/us-16-Mandt-De...
Pretty darned awesome.
Fiasco is GREAT. You at least used to be able to run it with DROPS which had a cool desktop/demo disk where you could just launch a bunch of Debian Linux instances as L4 tasks. It was like VMWare on crack at the time when I tried it.
I think FiascoUX might still exist... you can run Fiasco as a userspace process on linux then run linux in ... oh I've gone cross-eyed..
http://demo.tudos.org/eng_about.html
It was one, cool-ass demo. I especially liked firing up VM's lightening-fast given I was reading people say they use containers since VM's are too slow and inefficient. Maybe the people building their favorite VM's just aren't good at efficiency. Build on L4/L4Linux instead. ;)
That's a feature of the reality distortion field.
I wonder why neither Minix 3 nor Fuchsia are using L4. (I guess they may have learned the main lessons from L4 and chose to write those few thousand lines of code themselves for flexibility and control. Strangely, nobody likes to talk about it.)