Mike Smith wrote:
> Is there ANY penalty for having a device in your config file
> that is not in your system??
Yes. It can take I/O bus resources, IRQs, and memory
that might otherwise be put to better use.
> I am inheriting a 40 machine laboratory. My predecessor
> decided to go to a single config/kernel for all machines
> I'm sure for administrative convenience. I'm trying to
> determine if there is any major penalty for using this
> single "source" for all machines.
It depends. Some legacy ISA devices are not capable of
being identified and having their drivers automatically
loaded; if these machines are "fully PCI", with the only
legacy ISA devices on the motherboard, it should be fairly
easy to move to using modules for everything but those
integrated devices.
In FreeBSD, you will find that almost everything but the
devices in the boot path are capable of being demand-loaded
only in the case that the hardware is actually present.
This means that if your config covers your disk controllers
on all your machines (this may mean several drivers have
to be ther), pretty much everything else can be left out,
so long as it isn't in the boot path (yes, the console is
in the boot path; so is the keyboard, etc.). So you could
cover all your ISA devices and boot devices, and let the
PCI probes identify the other drivers that need to be loaded.
> Since we are doing significant hacks on FreeBSD to support
> proprietary FAA protocols and equipment obsolete to the rest
> of the world, I want to have as clean a kernel as possible
> to start from.
Cool project.
I suggest you build a netboot floppy, and then set up the
test image load, with all modules, on one machine, and
then netboot all of the PC's from an NFS export of that
image (one at a time, of course). This will let you
verify that you have the minimal necessary drivers to get
your network and the disks recognized, and from there you
should be able to decide on the proper "cut down" image.
If you were really lazy, and knew perl (aren't those actually
synonyms? ;-)), you could just netboot the full image, and
save the dmesg off onto the server (e.g. dmesg.<MAC address>),
and then process them all to get your minimal spanning set,
and do a "hardware survey" of the equipment. If you then
included only the list of hardware in the boot path, you
would have your "minimal kernel config", based on the probe
messages at boot time.
Actually, this would probably be damn useful to a lot of
people...
-- Terry
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