That might still be an argument in favor of microkernels if the Linux process can't crash the machine or cause it to miss hard-real-time deadlines. Or if you can use it to confine malicious code in the Linux process.
Fair, but when people talk about "real systems" built with micro kernels, as often as not, it could also describe Linux on xen with a watchdog restart. It's not especially compelling evidence that micro kernels are practical. Want to convince me that micro kernels are the bomb? Tell me about a system where no single service exceeds 40% of the code/runtime.
"Unikernels" is the misnomer being promoted by MirageOS for applications compiled to run on Xen, which they are currently doing on Amazon EC2 hosts alongside Linux instances. There are EC2 hosts that host a number of instances, including "unikernels" and Linux instances, and although I don't have details, the pricing on the smaller burstable instance types makes me think that some of the EC2 hosts are hosting actually quite a large number of instances, in which no instance exceeds 5% of the code or runtime. Is that what you're talking about?
No. What I mean is a micro kernel pace maker where 40% of the code is the beep beep service, and 30% is the meep meep service, and 30% is the bop bop service. As opposed to 99% of the code in the Linux service and 1% of the code in the realtime watchdog restart service.
Calling EC2 a micro kernel success story also seems like quite the definitional stretch.
Incidentally, I'd love to hear bcantrill rant on unikernels sometime, if he hasn't already in a talk or interview somewhere. I imagine he's not a fan, since they can never have the observability or performance of OS containers running on bare metal.
