Public SourceMage Discussion List

["Sergey A. Lipnevich" <sergey AT optimaltec.com>]

Andrew wrote:

> Well from a functional standpoint they are essentially the same thing
> except you dont get to try a new kernel in a chroot. However the linux
> spell is tested very heavily anyways so its a bit irrelevant (and
> difficult) to have the tinderbox test it. Is there any other bonus from
> using a UML kernel other than its elegant?
Well, that may very well be a reason ;-). Also, it may be easier to 
maintain.

> If we look at things from a efficiency standpoint I'd put my money on
> a chroot. A chroot simply remaps some of the values in the chroot'ed
> process's tables, and thus all its children as well, thus incurring
> essentially no time penalty and running the same as non-chrooted
> processes in terms of efficiency. A UML implementation, to my knowledge,
> runs a linux kernel as a user land process. This means that any process
> running under this user-mode kernel will eventually make system-calls
> (thats what a kernel provides), these system-calls in the userland
> process will eventually traverse through our user mode kernel down
> through some idealized hardware and come back out the other end, where
> might this be? well system calls on your native kernel, which then
> have to run through a whole mass of stuff (again) before it gets to
> real hardware. So you are essentially incurring unnecessary overhead,
> and throwing cpu cycles out the window (IMO).
If you look at the whole tinderbox idea from efficiency viewpoint, it's 
a complete waste of everything.

> So we have what amounts to something that is functionally very similiar
> but less efficient. If someone has benchmarks to correct me I'd be
> willing to change my opinion of course.
Testing is never efficient IMO. It never gives you immediate return on 
any investments, including time and resources.

> Although, I dont think we should rule out UML, we are about choice of
> course. Im just trying to point out the relative merits of one approach
> to the other, and lets face it, we want to be using every spare cycle
> as best we can!
>
> On a side note, I've made significant headway in a beta-version of a
> tinderbox. Id like to collaborate on error reporting and stuff with some
> people though.
Cool.