Performance of microkernel vs monolithic kernel

Problem Detail: 

A microkernel implements all drivers as user-space programs, and implements core features like IPC in the kernel itself. A monolithic kernel, however, implements the drivers as a part of the kernel (e.g. runs in kernel mode).

I have read some claims that microkernels are slower than monolithic kernels, since they need to handle message passing between the drivers in user space. Is this true?

For a long time, most kernels were monolithic because the hardware was too slow to run micro-kernels quickly. However, there are now many microkernels and hybrid kernels, like GNU/Hurd, Mac OS X, Windows NT line, etc.

So, has anything changed about the performance of microkernels? Is this criticism of microkernels still valid today?

Asked By : mmk

Answered By : Adam Maras

As is always the answer (or at least the preface) to performance-related questions: know your problem domain, run comparative benchmarks, and remember what premature optimization is.

First, no comprehensive benchmarking trials have compared monolithic kernels to current-generation microkernel systems that operate in an equivalent manner. So, while there may be trials that compare specific elements of those kernels, they're not going to be representative of the "big picture" that your question is looking to paint.

With that being said, there are wildly divergent observations of kernel performance across microkernels; for example, the L4 microkernel family can be said to have IPC performance an order of magnitude higher than the Mach kernel. But every Apple device from this decade is running Mach, and they seem to work plenty fast, right?

The moral of the story is that anybody who's deciding what kernel architecture to use needs to first decide what their ultimate goal is. Microkernel systems are (when properly implemented, of course) more secure, maintainable, and modular. However, they can be tough to architect properly, and may have performance overhead over a monolithic implementation. A monolithic kernel will be faster, but security will be harder to implement and it will be less modular and less easy to customize.

Your kernel architecture should be based on what your end goal is.

_{(And when all else fails, try it both ways and see what happens.)}

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Question Source : http://cs.stackexchange.com/questions/29854