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A comment on The Linux realtime preemption endgame is near. Parent comment

Re:The Linux realtime preemption endgame is near by adastra22 on Thursday November 16, 2023 @08:57PM (#38298322)
L4 was developed in the 90's. Operating Systems like Amoeba, which were fundamentally capability-based to a degree that even exceeds L4, were a hot research topic in the 80's.

L4's contribution was speed. It was assumed that microkernels, and especially capability-based microkernels were fundamentally slower than monolithic kernels. This is why Linux (1991) is monolithic. Yet L4 (1994) was the fastest operating system in existence at the time, despite being a microkernel and capability based. It's too bad those dates aren't reversed, or we might have had a fast, capability-based, microkernel Linux :(

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Re:The Linux realtime preemption endgame is near by josephg on Friday November 17, 2023 @07:49AM (#38302784)
How did it achieve its speed? My understanding was that microkernel architectures were fundamentally slower than monolithic kernels because context switching is slower than function calls. How did L4 manage to be the fastest?
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Re:The Linux realtime preemption endgame is near by vacuity on Friday November 17, 2023 @10:00AM (#38304451)
Two factors are the small working set (fit the code and data in cache) and heavily optimized IPC. The IPC in L4 kernels is "a context switch with benefits": in the best case, the arguments are placed in registers and the context is switched. Under real workloads, microkernels probably will be slower, but not by much.
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