ukernel complexity metrics

Espen Skoglund esk at
Thu Feb 24 16:40:58 CET 2005

[David Leimbach]
> 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?

Our system call ABIs are typically pretty much optimized to hold as
many relevant parameters as possible in registers (so as to avoid
memory accesses).  You could of course percieve a solution where parts
of one register holds the "sycall type" and the remaning registers
have semantics depending on this type.  I don't see how this gains you
anything at all (appart from consuming some register real estate and
requiring a demultiplexer---not relly what I'd call gains).  If you
know that you are performing a completely different operation you
might as well jump directly to the routine that implements that

As Jonathan pointed out, there can be other reasons for having a
single syscall, though.


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