Linux-kernel mailing list archive 2000-23,: Re: linux and micro kernel

# Re: linux and micro kernel

yoann@mandrakesoft.com
09 Jun 2000 16:27:10 +0200

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James Sutherland <jas88@cam.ac.uk> writes:

> On 9 Jun 2000 yoann@mandrakesoft.com wrote:
> > James Sutherland <jas88@cam.ac.uk> writes:
> >
> > > In theory, this is a good thing; in practice, it doesn't gain you very
> > > much. If my network server's NIC driver collapses, and it's running in
> > > usermode, then the server could continue serving files - except... it
> > > doesn't have anywhere to send them! It's effectively dead anyway.
> >
> > humm, you're talking about a configuration where there is > 1 machine,
> > and where each machine is a server ( for exemple disk server, sound
> > server )...
> >
> > What about the same problem if there is only one machine :
> > You have no NIC anymore, but the system stand up.
>
> The absence of network access from my machine isn't quite as serious as a
> kernel failure, in that I would usually be able to save any unsaved
> documents in the former case (assuming I was running the software
> locally). If I'm running software over the network, with a local swap
> device, I'm stuffed without network access. In fact, the loss of anything
> other than perhaps the sound card means the machine dies anyway.

Not only the sound card :
mouse, TV card driver, Video driver ( just remote login via the network ),
and i'm sure there is other exemple...

>
> > > Similarly storage drivers, I/O drivers, etc. OK, there are a few
> > > "expendable" drivers, where I can continue without them - sound, video,
> > > mouse, perhaps. However, if this is a desktop/workstation, I need to
> > > reboot anyway;
> >
> > why ?
> > just restart the faulty server, you do not need to reboot the machine.
>
> If that's possible. How do you reload a failed hard drive driver, for
> example?

Yes, it depend on the kind of driver :)

> A driver may collapse due to internal bugs, but normally the
> cause is duff hardware; only a hardware reset will clear that. (Sometimes
> not even that.)

You can't do anything against hardware faillure, but you can handle
software faillure....

> > > if it's a server, what does it have a sound card or mouse
> > > for in the first place?!
> >
> > misunderstanding : here, when i'm talking about server, i am talking
> > about one entity on the machine which is the ressponssible for such
> > or such system task ( eg : sound driver )
>
> I'm using the usual meaning, and using "driver" to mean driver.
>

sorry, i was wrong :)

> > > > The advantage is that there is really not many chance for the kernel
> > > > to crash, as it only do minimal thing.
> > >
> > > It's a nice theory, but in practice you need the device drivers working
> > > anyway.
> >
> > It depend on which driver...
>
> Not many of them are expendable. If I'm running a program over the
> network, the loss of my NIC, video card, I/O or storage systems mean I'm
> SOL. I don't really gain much in practice from a microkernel approach.

video card -> login remotely...
I/O storage -> you're dead :)

>
> > > Having "the kernel" working, but the machine being isolated from
> > > the outside world with no network or disk access, isn't much different
> > > from the kernel being dead as well.
> >
> > Humm, i prefer having a network card down, because of a bug in the
> > userspace NIC driver server which i just need to restart...
>
> Assuming, of course, you CAN restart the NIC driver. It could have caused
> a PCI bus lockup, in which case you are SOL anyway.

agree.

>
> > > > If a driver crash, it doesn't disturb the kernel.
> > >
> > > No - but it does cripple the machine as a whole, so it might as well take
> > > the kernel with it.
> >
> > well, why ?
>
> Why not? :-) If the loss of the driver disables the machine anyway, I'd
> rather panic the kernel (causing a reboot, if that's how I want panics
> handled), which will bring the machine back up in a known state.
>
> Microkernels are one of those ideas which sound very good, but don't
> really work in practice: there's a performance hit from all the ring
> transitions, and you still gain little or no stability. since the loss of
> most drivers is "fatal" anyway.

You gain the ability to handle software faillure :)

    --
    		-- Yoann http://www.mandrakesoft.com/~yoann/
     It is well known that M$ product don't make a free() after a malloc(),
    the unix community wish them good luck for their future developement.

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