On Feb 24, 2005, at 6:52 AM, Espen Skoglund wrote:
[Jonathan S Shapiro]
On Thu, 2005-02-24 at 09:15 +0100, Ronald Aigner wrote:
I disagree with the opinion that the complexity of a microkernel should be measured by the number of its system-calls. I find it rather complex to multiplex dozen flavours of IPC via one systemcall.
I am not sure quite what motivated this comment. We have argued in the EROS design that having exactly one system call ("invoke capability", in our case) is good, but not because it reduces microkernel complexity -- in fact, it complicates it.
Would also like to add that the reason for multiplexing all these operations in the IPC mechanism is not really to reduce complexity. We multiplex all these operations because the operations are similar enough in nature to share the same codepath and thereby reduce the cache/memory footprint of the kernel.
I don't think anyone has ever stated that the number of system calls is a measure for the *complexity* of the kernel.
Just to chime in quickly here... At the most primitive levels of the kernel everything can be multiplexed to one system call and I don't think this would really "bother" me in trying to understand how to use the kernel because it always seems that someone comes along and wraps that one system call with normally very lightweight abstractions to help demystify the heavy amount of multiplexing.
In this way that perceived complexity can be reduced with little overhead.
Can't this sort of thing be "generated" either by macro or IDL to add an artificial abstraction layer to make it more clear to the higher level L4 coder what exact functionality is being called upon?
I'm not sure I see how heavy multiplexing has to be a problem for anyone. If it's possible to do it all in one syscall, I'd go for it :). After all increasing the complexity of the upper layers is traditionally what modern microkernels do but once you have a really decent library of tools I bet a lot of the perceived complexity falls away. [maybe not so much as to make it as "easy" to code for as a monolithic kernel but good enough :)]
Is this consistent with the current philosophy of microkernels?
Dave
eSk