[nycbug-talk] kernels

Bob Ippolito bob
Thu Jun 3 16:43:52 EDT 2004

On Jun 3, 2004, at 3:27 PM, Pete Wright wrote:

> yea this is crazy.  this bantering doesn't even relate to the 
> article/thread either :(  i was hoping people would more interested in 
> the micro v. monolithic kernel issues, esp. seeing that apple has 
> adopted MACH.  sigh.

Personally I prefer microkernel architectures because they're easier to 
work with (as a developer).  They also offer loads of practical and 
theoretical advantages.  The discussion in the article is really about 
modular versus static (an implementation detail), not micro versus 
monolithic (a major architectural decision).

The security argument is kind of silly, because if that really was a 
concern you could add a sysctl that lets you turn module loading off 
(forever) at runtime.  So you boot up, load your modules, and turn 
module loading off.  In practice, nobody really does this (as far as I 
know) because only root can load kernel modules and root can do 
whatever he wants anyway, whether or not the kernel is split into 1 or 
1000 pieces.

The supported configuration argument is also silly.  The only 
difference is that OpenBSD is only configurable at compile time, where 
others are configurable at runtime.  Since it is open source software, 
the user is still free to alter (or more likely, NOT alter) that 
configuration in both cases.

However, with the development tools we have today, static kernels can 
offer several obvious slight advantages.
- marginally better performance on average
- easier to install/upgrade (just one file)
- can be easier to debug with tools that don't know what kernel modules 
are (the addresses of symbols never change)

All three of these are minor though.  The latter two are solved with 
better tools (that pretty much already exist), while fixing the first 
could be lifted with a lot of work by using JIT techniques.. but it 
would be really hard to implement correctly and the performance 
improvement is very marginal.

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